Electrical Dilemma

J

Jazzmanic

New member
So I've been running this over and over in my head and decided to ask the experts from the Pub.

Last summer while on the hook with our C-Brat buddies in Desolation Sound, I tried using my CPAP using the 12v plug after a few days without charging the batteries. Despite trying to reduce the power draw settings on the CPAP, I ended up fully discharging the House Battery. Since I installed the Blue Seas Add-a-Battery system which is an ACR (or VSR) system, the Start battery was isolated and was not discharged. However, since all my electronics were connected to the House Battery, none of my electronics (most importantly 2 GPS and the VHF Radio) were working as we traveled about 10 miles to Gorge Harbour. Luckily I had GPS on my phone but I started to lose my battery on that as well. We had nautical charts as well but no means of communication either by phone (out of range) or VHF.

I had never before run down a battery since owning C-Dancer and was a little worried that the Start Battery would go too but the ACR did its job of isolating the Start from the House battery and we made it to our destination and were able to charge the House Battery back. I received stern advice from the others saying that one should never compromise the GPS and VHF radio and that those at the very least should have been connected to the Start battery rather than the House Battery.

So I'm asking, what should I do? What do others do?

1) Connect the vital electronics to the Start Battery? That was my first plan of action and I have even purchased all the electrical supplies but am holding off to get more advice from boating experts here at the pub.

2) Buy an AGM battery and charger to be stored in the cabin and connecting the vital electronics instruments to that.

3) Skip the first two above since I'd never had a problem with the configuration prior and buy a generator/inverter to be used during the times we're on the hook (which is rare) and for use in either powering the CPAP or recharging the batteries.

4) Or do nothing, it was an aberration. To repeat, in 11 seasons I never ran down the batteries even once and this only occurred because I used a power hog CPAP for the first time. Meaning the current configuration has worked fine all these years.

I suppose I need to do something because I will be using the CPAP on the hook at one time or another in the future. What say you?
 
Hi Peter, you must have your electronics attached directly to your house battery, I know it's done. Better to have a Buss for your electronics and power it off your common post of the selector switch, this way no mater which battery you're using, you have power to the electronics.
I use a Buss bar up behind the helm for all electronics, powered off the main line coming from the selector switch in the lazaret
Hope it helps
George
 
Peter, another option you did not mention is one or more solar panels to keep your house battery charged. Maybe you should increase the amp hours on the house side, maybe two six volt golf cart batteries in series charged first by the alternator through the VSR, then solar, then a Honda 1000 watt generator as a final backup. You also should look into a Victron battery monitor - knowing the state of charge and when you need to do something about it - is very important to us. What you do ultimately depends on the power requirement of the CPAP, I know our freezer would drain the house batteries (two 12 volt batteries in parallel) if we stayed at anchor for an extended time if we did not have the solar panels. On your question, I am not an expert, but I do NOT want anything on the starting battery except the outboard engine. Address everything else by maintaining a good state of charge on your house batteries! Good luck!
 
I have had several questions about CPAP. You can cut the current down by turning off heater and dehumidifier. But they are going to use more power than the average battery can handle, over several days. You are now due a new battery.

First. Get a battery voltage monitor. They start at $3 on Amazon. You can even get one which shows amps watt hours etc for about #15. Best to get a Victron monitor (a bit more)> Do not discharge batteries to less than 12.2 volts resting state. When the voltage is down--run the engine to get them back up, buy a generator (EU 1000) and run it to charge the batteries--with a bigger charger than what is built in the boat.

At the very least buy a digital volt amp meter, and learn to use itl.

In the case you had, start the engine. Then wire the main wire to the panel to the engine starting battery. Most likely you can do this with the 1/2/0ff switch. If that battery was truly shot, then the VSR /ACR may not be able to put a charge into the house battery. That would take some investigation

Yes solar panels would help, but not as much as at Lake Powell, where there is a lot more sun!

Another option (basically what we do with the freezers) is to get a 3rd battery, just for the CPAP. Also is it worth while getting the lowest draw CPAP, if you don't already have one.

Innovation, and flexibility are also key.

Should the electronics be wired to the engine start battery? When I have 2 batteries, they are not. Because the low starting voltage and initial spikes from the higher charge output may be hard on them. I learned that lesson the hard way in the late 60's when the first wind instruments came out--fried them because of that.

After the engine is running-OK to connect--so a transfer switch to them would be fine. Notice that when you start the engine==many of electronics will stop, and have to be re-started.
 
Peter,
Bob has great advice as always...a simple cheap voltage check can save your bacon. An expensive instrument with complex installation and lots of buttons is even more fun.
I learned the hard way in the late 90's EXACTLY what he learned in the 60's.
Some things don't change much.
I don't quite understand why after you got your engine started, you didn't just rev it up to 2k-2500 RPM for a while in neutral to charge the House battery enough to run the helm (10 min?), or manually Combine them or let the ACR do it for the run back.
If the battery is good, a one-time discharge for a known reason is not enough to spend a lot of money on this issue. On the other hand, spending a lot of money on your boat for a not real good reason is perfectly reasonable, if like me you like to do that sort of thing and don't have competing expensive hobbies, like flying antique jet aircraft or golf.
A Honda 1000 is a cool boy toy even if you don't quite need one often.
I have 2 Honda 2000iu's which I haven't needed since Katrina, but boy they sure were worth it then. You would not believe it how all the neighbors will will give you their gas in exchange for frozen Margaritas and ice when you can't get either one from FEMA.
Plus, the ATF agent next door guarded them with his AK-47 and let me use his gov't sat phone to call Mom since I kept it charged for him.
Whatever floats your C-Dory.
Cheers!
John
 
Not sure what brand Cpap you use, but I have the Resmed S9. There is no 12 vt adapter. However, with the humidifier removed, I run it off a 100 watt inverter plugged into my cabin accessory outlet. Running it all night (8 hours), along with using 2 of my LED cabin lights for several hours, and even an LED Anchor light, I have yet had any problem starting up the next day. I just recently installed a webasto heater, and waiting to see how well the battery holds up running that over night as well. (I have two batteries, one I think a group 24 the other 27. (I THINK). At night, I normally run off the larger battery. So I still have the smaller one to start from, but routinely just leave my battery switch where it is when I start up the next day. This probably doesn't answer your question, but have you thought about getting a newer cpap? (And if you are using a humidifier, I'd definitely turn that off while running on the boat.) Colby
 
Roger, There certainly advantages to low battery alarms--in fact I just got back in the house--a neighbor's boat has an alarm going off. I have no idea what it is, except is is not on fire, and not sinking (no wanter in the bilge). It could be a low voltage alarm--We will find out, when the owner gets back to me--IM, cell phone and computer don't get to him...

The Siren system is a complete boat monitoring system, and works very well. Expensive..

The Aqua Alarm (I have a complete inboard system for sale after the garage clean up). has a set voltage of 11.7 volts--a dead battery.

The first one, does have adjustable alarms. I prefer to look at the voltage every few hours. An alarm may go off during s sudden voltage drop. The monitoring systems do draw a small amount of current, but eventually can draw the battery down, if you don't have a charger on. But a good idea, if you don't want to watch your batteries.
 
Hi Peter, I love battery puzzles.

A few questions come to mind here.

What is the age and size of your house battery??

Were you ever able to power up the chartplotter and radio? Perhaps after the first few minutes or a bit later?

What is the age/condition of your starting battery?

What other power saps do you have on the boat?

Don't connect accessories directly to the start battery unless you don't have other choices Consider the bus bar setup mentioned above if you do have direct accessory connections to the house. Monitoring is a good idea whether you go simple and watch voltage, or go fancy and watch amp hours.

Greg
 
For what it's worth here's my CPAP / battery experience.

We are preparing for a summer of truck camping to Nova Scotia and Newfoundland. I plan to take my CPAP (Resmed Airsense 10, 24V) device but I was concerned at how much power it might consume.

The device runs on 24V, and by the time I tried to calculate the electrical consumption but after factoring-in everything (converting 12V to 24V, amps consumed, and all that jazz), I was totally confused. I even asked Dr. Bob for help, and although his response was great; I was STILL confused.

I figured there MUST be an easier way....

The boat batteries are both sitting in the garage. My theory was to take one of the fully charged batteries (Duracell AGM - SL34MAGM) and perform a "test." I took a battery to the bedroom and hooked-up the Resmed DC Converter to see how much battery power was ACTUALLY consumed. That worked like a charm. Here are my test results:

MON (1600 hours) 12.69V [possible erroneous voltage reading]
MON (2030 hours) 12.88V [CPAP connected, voltage check]
[sleeping]
MON (2130 hours) 12.67V [CPAP connected, voltage check]
[sleeping]
TUES. (0415 hours) 12.58V [CPAP connected, voltage check]
TUES (12Noon). 12.55V [CPAP connected, voltage check]
TUES (2100 hours) 12.49V [CPAP connected, voltage check]
[sleeping]
WED (0800 hours) 12.23V [CPAP connected, voltage check]
WED (1500 hours) 12.20V [CPAP connected, voltage check]
WED (2100 hours). 12.17V [CPAP connected, woot age check]
[sleeping]
THURS (0700 hours) 11.90V [CPAP connected, voltage check]
THURS (1345 hours) 11.86V [CPAP connected, voltage check]

As you can see, I kept the CPAP "connected" thru the entire period, including four nights of sleep. As far as I know the humidifier(warmer) feature was turned "on" but I seldom use it (there is an automatic feature that turns-off the humidifier if there is no water in the reservoir).

All-in-all the Resmed CPAP seems to use much less power (even at 24V) than I was expecting. With this info in mind I am pretty comfortable taking power directly from the truck battery for overnight CPAP use and rely on the running each day to recharge the battery. (But I still may take and emergency 'start battery.)

...did I forget anything?

Best,
Casey&Mary
 
I have a inline switch in my AC line and will have one in my 12v line as well.
The Resmed does run at a very slow speed when not being used. ( at least mine does )

Bill Kelleher
 
Casey's example (thanks Casey!) is using a relatively small group 34 AGM battery rated for 55amp hours at the 20 hour rate. Many of you have group 27 or larger units with capacities in the 70-100amp hour range. It looks like he got two solid nights worth of use with no other draws so that is a starting point of reference for that CPAP unit.

Reminds me we have too much power, Bring on the freezer!

Greg
 
We used two group 27 batteries on our previous boat. One was start and the other was the house both deep cycle. A simple manual battery switch 1 2 or both. When away from power we just set the switch on one battery. We used a 400 watt inverter that plugged into a 12vdc socket. Then a six way power strip plugged into the inverter. If the battery got low the inverter would go on overload and screech out an alarm you would not be able to ignore. We use a Res Med C-Pap machine also and never had any problems. We usually only spent a night at a time off the grid. Like Bob recommended a solar panel or a Honda generator might be in your future if you want to stay out more extensively than a night off the grid. We always carried a Honda 2000 for backup. That way we just plugging our shore power cord via adapter to the generator and let the boats battery charger do it's thing.
Our new boat has a two house battery bank another battery for the thrusters and a start battery all the same size and a switch to combine all if need be. Each bank has it's own separate on off switch The solar panel seems be able to keep up with things including a refrigerator freezer although some combine the two house batteries with the thruster battery giving them more power for multiple days on the hook. Even though I have a 1500 watt inverter that came with the boat I still use the little 400 watt inverter for my sleep machine and our charging phones, Ipads and camera batteries etc. when not connected to shore power. I don't want too start using the microwave etc. off the bigger inverter as I believe the bigger inverters are battery killers. Plus the ever present generator makes us feel like we have all the bases covered.
D.D.
 
I was just looking into how I will monitor my batteries. I don't need anything very complex on a CD 16 and was looking for the tiniest monitor available. I just ordered one of these.

http://www.ebay.com/itm/171898210875?_t ... EBIDX%3AIT

It could be permanently mounted, or put one on each battery, or, using alligator clips, to diagnose voltage drop issues around the boat. You could even put one in the V berth, or even in parallel with the CPAP, so that you can see the state of charge during the night. All for $1.43 including shipping from China.

Some day we (or the next generation) will pay a very high price for this "free" stuff from China.

Mark
 
Wow, all great answers! I'll try to provide the details and recreate the scenario I was facing when the battery failed.

3rd day on the hook, no battery charging before the trip as the boat is stored at Twin Bridges (indoor stack with no outlets)

Deep Cycle Battery - Interstate SRM-24 installed May 2013
Start Battery - Interstate XHD-24M - installed May 2013

I did have a DVM installed in 12v plug in - I'm sure I checked the voltage prior to using the CPAP on that 3rd night but can't remember what it showed.

CPAP - ResMed Air 10 - DC 24v - 3.75 amps
ResMed 90w DC converter - DC output 24v -3.75 amps

Switch system - Blue Seas Add-a-Battery - installed exactly to specs
No direct connections to batteries except to switch and battery cable to positive and negative bus bars for each battery

I did turnoff the humidifier before hand, no other power draws during the evening except Perko Anchor light

When I took off the next day, no problem starting. About 5 minutes into the trip, noticed the GPS kept turning off and wouldn't stay on. After a few more minutes no power from GPS and VHF, concluded discharged battery. Plugged in DVM and noticed very low reading but don't remember exact number.

So to conclude, I'm assuming after three days on the hook and no prior recharging, the house battery was already discharged quite a bit, probably less than 50%. So the power drain wasn't entirely due to the CPAP but more likely due to the state of the battery voltage after several days on the hook.

The Blue Seas ACR is set to charge both batteries while underway, EXCEPT if one of the batteries drops below 9.5v at which time the ACR closes. I take that to mean it will not try to charge the discharged battery.
Add-a-Battery diagram
Click on the different scenarios in the middle of the page. Am I reading that correctly?
I did not try to combine the batteries while underway as I was afraid of discharging the start battery.

So.... here's what I think I should do after all your great advice.

You all confirmed my intuition that I shouldn't be connecting additional devices to the Start Battery, so I will probably buy an AGM battery to be stored in the cabin and connect a 12v outlet to it for use with the CPAP and probably a couple of other electrical items that don't get used much (seems a waste to use the battery only once a year for once device) but not the VHF or GPS. I will buy a hand held VHF so I won't have to worry about that going out. And if I anticipate staying out on the hook for days at a time, I will purchase a generator/inverter. I've been looking at the Ryobi RYI2200 2200 watt digital inverter generator. They're available for a great price on Amazon and seem to compare favorably to the Honda 2000. I will probably wait on the solar panels Pat. And obviously I'll do a better job of monitoring the battery voltage while on the hook and calculating the amperage draw of the devices in use.

Thanks all! Peter
 
First batteries we will assume a high quality "Dual Purpose" battery 20 hour rating; Most c Dory come with group 24 batteries (amp hrs: 65) often a good compromise is a group 27 (amp hrs: 80), or best a group 31,( amp hrs 105) The group number only means case size. Generally a heavier battery will be better.--more lead. You only want to take 50% out of a battery, so you don't want to discharge it to less than 12.2 volts. (Since it was running the CPAP, the battery voltage would have seen lower than the "resting state". But best to stop at 12.2 volts, to avoid damage to the battery, "Deep cycle" group 24 batteries, as sort of a crock...real deep cycle batteries are going to be like Trojan T105, 6 volt Golf cart (2 in series to = 12 volt) Better yet, Rolls Surgett which are much heavier, or L 16 floor sweeper cells.

Next "Charging batteries" If you just run the batteries on the engine--most likely you will never fully charge them. The only way to know will be an amp in and out meter. Can do a fairly cheap, or go with the Victron. If you have a volt meter--use it! Learn what it means. You might say what about our cars? Well, most of us run a cars almost every day--and run them a lot more than the boats. On the boat, either top them off with solar, a generator, or shore power, at least every few days.

Again--if you don't top off the batteries, you are harming them. They will not last as long, or give as good service. If away from mains power--get a small solar charge. I stored the boat and a van out west, and it would be 6 months between visits. Batteries were always topped of--solar panels!

Every battery off the engine usually comes to the last 20% of capacity--20% is a lot! you have to go thru the Bulk and Absorption phases, and be at the start of the float stage. Different batteries have different profiles, you have to take into account the temperature of the battery, if charging heavily.

The 3.75 amps at 24 volts = 7.5 amps at 12volts (plus some loss in the converter) . If it is using that much, then you are going thru the battery overnight! (This is why it is necessary to get a good meter to measure just what you are using.) Casey's way works OK also. This 3.5 amps@ 24 volts is the max power consumption and output--not what is being used all of the time. Wiring and fuses should be speced to this. Inverters have some inefficiency--some where in the 90% + efficient. The inverter sized for the load is best.

Back to Jazzmanic: Still want to have manual way to connect start and house battery. Can be a simple switch for an emergency assume you stay with 2 batteries.

AGM--yes, if inside--where are you going to put it? But if only once a year, there are other options, such as solar, plug into power, etc.
I believe that the below 9.5 is true--but that battery is now damaged--and has been be being left at a partially discharged rate. Might be brought back with pulse tech. But I would tend to replace it. (3 years old--I get 4 to 5, sometimes more).

Parasitic drains. Many boats are wired, so that GPS, radio, stereo etc all have small current draw. Same with volt meters which plug into a socket. same with what Marco is considering. For that there is 23 milli amp per hour. That is almost 3/4 amp in a 24 hour day. Not a problem on a daily basis. But over a month--battery is dead. So when not using radios etc, be sure they are completely off no memory! reset the FM channels, etc. Marco, you put 4 of these around the boat, and now you are using almost 100 Milli amps an hour! Sure seems picky, but it all adds up. Even for these little volt meters, I think they are best used with a push button switch, to get a voltage. If your not looking at it--why have it on?

As for the Ryobi. Save your money up for a good Honda or Yamaha, if you want a generator. Even the EU 1000 will do almost everything you want on a small boat. It will run a 5,000 BTU air conditioner, charge @50 amps for 12V batteries, run a induction burner (at a medium setting). Read the reviews on people who have issues with the Ryobi. Look at getting engine parts. A Honda is good for years-thousands of hours. I have one which is 30 years old --550 watts steady--800 surge. It has charged batteries and run lights for many hours. Still runs fine. I have some Ryobi tools, I like their batteries (Li Ion), but I know that these are not long lasting tools. I have good tools for the shop at home, the Ryobi are "traveling"--and if damaged or lost, I don't worry.

Casey good numbers. What I was suggesting to Casey that if there as an issue to put a second battery in the truck, run it off a VSR, so no chance of damage to the truck battery or getting stranded. This is what we do in our truck, with the refer/freezer.
 
Hi Peter, and all,

(NOTE: You posted your post as I was writing mine so there is some new info there. I will address that here in Italics and then my response to your original post will be below that.

Mostly regarding the battery state prior to your trip. I was probably down, and though I would have thought it would have charged on you run over to the anchorage, due to the connected regulator, it may not have. That would mean you stared on an already somewhat discharged battery. Your proposed fixes look expensive. Another possibility could be to either, pull the battery to take home and put on a BatteryMINDer, or similar device or put in a charging system to charge the boat batteries while towing. I might go with a larger battery set, (Group 27 or 29 Deep cycle) rather than adding a third battery and all that it entails.

I think it is "curious" why you had GPS and VHF on starting and then 5 minutes into the trip, those went south. Seems to me like the outboard should have been providing charge power to that battery if the switches were in the right places. (ACR or 1-2-all). As a usual practice, I do a battery level check prior to starting the OB's. Once they are started, then the electronics are switched on, in a specific order, with the plotter being the last in line so it does not get fluctuations from the other devices coming on line, and by then the OBs are on long enough to have stabilized their alternator output.

I would recommend having a portable handheld VHF on board, no matter what else you come up with.

Now back to the original answer:


Ahhhh, CPAP on the boat. Well it should be CPAP every night; so CPAP on the boat should not be a question, right? Want a good night’s sleep, (if you have Sleep Apnea) then you need to use your CPAP. Sleep…. One of my favorite subjects. Rates right up there with C-Dorys.

Some Disclosure: I have Obstructive Sleep Apnea, and to get a good night’s sleep, and wake up refreshed and without a headache, I use a CPAP set at 17cm H2O, or an Auto CPAP set at 6-17cmH2O. I am also a Registered Polysomnographic Technologist. In plainer English and most of my friends, that’s “Sleep Guy”. Working in that field allowed me to fine tune my treatment very accurately, and have access to a pretty wide variety of equipment. In looking at my pressure record for a night I found I needed the 17 very rarely, usually only once a night. At 15cm about 40% of the times I needed pressure, the4 15 was the maximum so I settled on using a pretty old, fixed pressure machine set at 15cm H2O. It is an old Respironics REM Star Pro and like the other older Respironics, it runs on a 12VDC Cig Plug, straight from the plug to the CPAP and by doing that I avoid the “power brick” transformer or using an Invertor, both of which cause a power loss of some value. I have used this system on SleepyC for going on 9 years. Never a problem and no dead batteries.

To be sure, I use a very cheap, battery level monitor that just plugs into the same Cig Plug and gives me a digital voltage reading. I can check either battery or the combined voltage by switching my “1-2-Both-Off” switch, which I do and log every morning and night. Running my CPAP for about 7 hours uses about 0.3 volts off my two group 29 marine deep cycle batteries that have 95 amp hours each. If my evening volt check shows less than 12.6VDC I will run my twin 40 Yamahas at about 1800RPM for long enough to bring the VDC up to 12.7 at least. Generally, If I run the engines for an hour or so, at even my preferred slow cruising speed I have plenty of battery reserve. If I hang at anchor for more than one night, there are times I have been able to do two nights without running the OB’s to charge up. (Again, I watch my monitor and use very little electrical accessories. If at anchor, I do use my Garmin GPSMAP640 for anchor watch, and maybe charge my phone.)

So Peter, Looking at your battery down situation, I would be tempted to not change a whole lot. If it were me, I would: #1. Be absolutely sure the heater and humidity settings are off. You can still put some water into the system but in some newer machines that will trigger the humidity (heater) to come on, depending on the settings. #2. Watch the battery voltage in some way. In your case, the house system for sure, since it is isolated from the start. #3. Care a jump start device of some sort. And #4. Don’t give up on the CPAP. Sleep apnea, untreated, has a HUGE adverse effect on our health and well-being. Props to you for using it and working on a system to make it reliable.

I would not recommend carrying a generator just to run a CPAP device off of for all night. To use one to charge the battery system via the onboard charger, or shore power system is fine, but I have real compunctions about running any Carbon Monoxide generating system overnight while sleeping onboard.

Solar power is often used successfully for charging the house or combined systems. Some are more effective than others due to system design and/or environmental conditions. Some CPAP systems are designed to be charged by solar energy, and can be effective adjuncts. There are small(er), portable batteries that can charge on 12VDC while you are running during the day, or charge off of shore power when plugged in there. Again, running an inverter to charge a battery is not the most efficient use of your 12VDC power but if the OB’s are running there is most likely sufficient voltage for that purpose too.

Spoiler alert: I am working on a “CPAP on D-Dory” thread posting to come up in the near future, so #1, I welcome questions, and #2, I recommend “Use it if you need it”.. which means that if you are supposed to be using it at home, you are also supposed to be using it in the boat or RV (or motorcycle) when traveling.

To all, A good Night,

Harvey
SleepyC :moon (Get it?)

1_10_2012_from_Canon_961.highlight.jpg
 
Peter, It sounds like there is one key element to your story and Bob mentioned some of the impacts. You store the boat indoors/racked at twin bridges with no shore power available for charging and no light for solar. That means your batteries sit for long periods, slowly discharging and becoming generally weaker while also not being peaked when you go to use the boat. If you are currently using regular batteries (not AGM) then you should consider switching to AGM before you do anything else.

Deep cycle AGM offers deeper safe discharge levels so you end up having greater power available overall without damaging the batteries or going up in size.

AGMs self discharge around 3% per month instead of 10% per month so they can sit and still be healthier and more ready for use.

With your storage situation, I would switch to AGMs (bigger only if you can fit them) and consider any possible periodic charging options you could pursue at twin bridges even if that means de-racking the boat and topping up the batteries with a shore connection for half a day every other month of the year while you do some cleaning or just have a couple of beers and tinker. This would also help recover from any small parasitic draws you might have on that boat that are making your storage discharge problems worse.

Not having shore power or at least a solar option, is a recipe for short battery life spans and that very well could have been why you ran into trouble.

You system layout is likely just fine and ready for better batteries and maybe some periodic peak charging to maintain battery health a get 5+ years of life out of a set.

Skip the third battery and just carry one of those new tiny jumper packs to jump your house battery back above 11 volts so your ACR can kick back in and charge from your outboard again. That would give you a backup in the smallest and cheapest form. One of these packs would have likely saved you during that trip and got the house charging again for the time being.

http://www.amazon.com/PowerAll-PBJS1200 ... B00D42AFS8

Greg
 
Good suggestions Greg. Forgot to mention I in fact installed a complete 30amp shore power system by the book including galvanic isolator and AC panel a couple of years ago when I had the boat at the Edmonds marina full-time. So I do have shore power capability and I charge the batteries every chance I get to plug into shore power. But you're right, it's the time that's spent stored on the racks that may be slowly discharging the batteries. In past years I've actually taken the batteries out and stored them at home for the winter, charging them regularly on the charger. I just checked on the boat for the first time in 3 months last weekend and the motors started right up. I should have run the DVM on both batteries during that time to see what charging state they're in. Next time, maybe in a couple of weeks. You see, since we almost always stay at marinas and very rarely anchor out for more than a day or so, we've never really had to worry about discharging a battery the whole time we've owned the boat (11 seasons) but as they say, it only takes one time. :sad

I like your suggestion about using AGM's due to the slower discharge rate. I might have to suck it up and score a few. If I do, do you suggest two of the deep cycle batteries rather than a start and deep cycle? I also like the idea of the little jump pack too. Thanks!

And Bob, thanks for your clear and instructive explanation, very helpful as usual. And thanks for the advice to steer clear of the Ryobi. The advice from all has been very valuable and has made me think a little differently about batteries after all these years.
 
One comment on generators and charging batteries. I agree with Harvey, never consider running a generator for a CPAP machine.

For generator charging, I choose a larger charger than what comes with the c Dory. (usually a 5/5 Guest charger--that is 5 amps per battery). That may take 20 hours to even get to a float stage (because of the the tapering off as a battery gets close to a full charge).

I happen to use a West Marine battery charger, made for marine conditions, but not made as built in charger. Mine is older than the more recently sold 30 amp #BC30WM. The newer one make auto compensation for temp--mine manually you put in the temp. These are "only" $140.

One other beauty of AGM batteries is that they will take a more rapid charge than a flooded lead acid battery. Basically I run this charger on my group 31 battery for an hour, putting out 30 amps. Then it begins to taper, and I tend to shut the generator down at about 3 amps charge. This is not fully charged, but getting to the 90% range, and is a good compromise. A number of times we have used this system for over a month of boating, with no mains power--and it works well. I am cycling the battery about 50 to 60 amps draw and recharge twice a day.

I get my AGM's from Sam's club--for me it seems like a good compromise price vs quality. Their AGM's are made by East Penn--one of the better manufacturers. The Odyssey are a better battery. They are 11# heavier than the Sam's club, they cost twice as much.

Advantages of the AGM battery; low self discharge as Greg noted. Can be placed safely inside the cabin of the boat, can be put in any position, except up side down, will take a greater charge, although they can be discharged more deeply, more rapidly--any battery will suffer some loss of life with extreme discharge. The Odyssey company gives a 450 cycle life at 80% depth of discharge.
They give 700 cycles at 50% depth of discharge. Is this important? Probably not for the average boater. Where it will make sense, is if there is full time use. In this case, then the very high end, Surrette/Rolls would be a better battery, they claim 3000+ cycles to 50% depth of discharge, 2000+ cycles to 80% depth of discharge, with a similar battery of 115 amp hour and cost of $375 plus shipping (not cheap).

Another good choice is the Sears Platinum Die Hard marine, which can be found on sale--and can be the "best buy" (also made by Odyssey.

One other option is to put a solar charger remote from the boat. I have no idea if this is possible at your marina, but this is what I did with my van and boat stored in the West. I was able to screw the panels on wood, which had good orientation to the sun, Amazingly no one stole them!
 
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