Battery Choices

colbysmith

colbysmith

Active member
Looking at replacing my batteries pretty soon, as they are now 5 years old and we do depend on them a lot with all our travels! I was thinking Optima for a while, but now mostly just thinking about staying old fashioned and sticking with the wet cell lead acid. Basically I want dependability and simplicity, without any additional weight. Nor do I want to have to mess with my altenator or charger. (2007 Mercury 115 EFI 4 Stroke, with I believe 39 amps of charging power at the battery if I remember, and a new 30 amp Mastervolt battery charger.) There are several older threads on batteries, but so many changes with current technology... so I'm starting this new thread. Not a lot of room on the CD-22 so also sticking with two 12vt batteries. I currently have a group 24 Marine Starting Battery and a group 27 Marine Deep Cycle battery stuck in my port and starboard lazarettes. More than likely I would go with the same group sizes, but perhaps a combined starting/deep cycle battery on both sides. Any recommendations or advice? if anything, it would be nice to reduce weight, but don't know about the high priced lithium batteries... Colby
 
We recently had one of our house pair of batteries give out at about 5-6 year mark and we run them parallel connected so that meant a new pair for us.

I wanted to go a bit smaller for easier maneuvering into the boat compartment so I switched from group 31 to group 24. I purposely sought out models with deep cycle design plus on the higher end of the capacity range and wound up with a couple of these as a "kit"

https://www.amazon.com/MR107-85-Marine- ... B01HDXEI5O

We have had them about a month and put about 10 days of freezer running shore powerless use through them and they are behaving quite well.
They seem true to capacity based on my victron monitoring setup and they were indeed much easier on me to install in the under-berth space of our 19.

You may not need the AGM type, but with your relatively high amperage charging rates, they may live happy a bit longer than the same size flooded battery due to better charge acceptance rates and the discharge ratio can be about 25% higher as well which is good if you have any regular amperage loads in excess of 1/4 your bank capacity. Being able to mount them at angles or on their sides could be bonus as well.

Greg
 
Unless you have won the lottery, I would stay away from the lithium batteries for your boat. They are getting cheaper--and at some point may be the only battery offered, but not today. It will cost you only $700 each to replace the group 24, equivalent battery, currently--2 years ago it would have been about $1500!

I like the Sam's club AGM's But I have group 31's so I am not in the weight saving mode. Mine are 3 years old, and testing as new still. My philosophy is to not discharge a battery to less than 12.2 volts or less than SOC 50%.

I like batteries by East Penn (which includes the Sam's club), and Sears Platinum.
Also Interstate is a good line.
 
I have a couple of interstate marine AGM batteries, 3 years on with no problems. I desired AGM because I moved my battery bank forward/enclosed for weight distribution which worked very well. These are very robust, with heavy duty posts and cases. Also totally sealed and can be mounted in any position or without ventilation. They cost ~ 175 each new.
 
Cost is an important factor also. Not sure the extra cost of AGM makes up for any improved performance they offer... but that's what I'm trying to decipher...
 
I also pursued the new carbon foam type (firefly) and they looked promising and around the same cost as AGM for similar capacity. But they were out of stock on this continent and would be about a 6 month wait which I was not about to do.

Greg
 
Aurelia":7ak1b8s2 said:
I also pursued the new carbon foam type (firefly) and they looked promising and around the same cost as AGM for similar capacity. But they were out of stock on this continent and would be about a 6 month wait which I was not about to do.

Greg
Click to expand...

Greg, the Sam's Club Duracell group AGM (East Penn, same as Deka), are $180.
The Firefly group 31 is listed at $486. About 2.5 more expensive. There may be cheaper sources for the Firefly. I would love to try them but the economics sided with the Duracell.
 
The Firefly cost comparing battery to battery is very high but that is a false comparison.

With the Firefly advantage being a lower safe discharge floor.

Two AGMs at around 100 AH each can be safely discharged to about 50-55% while still providing a multiyear life to the average boater.

One Firefly at 110+AH can safely be discharged between 80-100% while still providing more than double the cycles of the AGMs in the above example.

Not to mention that charge acceptance is greater (less resistance) below the 80% SOC mark so the firefly would also cycle more efficiently in real use (batteries charge with less resistance at lower battery levels).

So I ended up paying 390 dollars for a set of AGMs providing 80-100 amp hours of usable capacity (typical, and a bit aggressive) that will likely last another 5 years...

Or

I could have paid another 96 bucks for a single Firefly battery with 90-110 amp hours of usable capacity that would likely last 10+ years and save me the weight and added complexity of the second battery.

Paying 360 vs 486 dollars (26% more) to gain more than double the lifespan while saving half the weight seems like a worthwhile investment. I also like the fact that your charging systems can remain the same vs lithium options that would require new charging equipment on the boat for most people.

If the Firefly units were not sold out, I would have gone that route for the weight savings alone and will surely be considering them next time I make a battery purchase.

Greg
 
Colby, for wet batteries, I just go to Costco. They're affordable and are seemingly of high quality. Boats, truck camper and travel trailer all have Costco batteries. I do have a small shell camper with an AGM, but haven't needed to replace it yet, maybe in a few years.
 
Excellent summary of the advantages of the Firefly; What Greg states above is for the most part true and valid. Where it may get a little dicey is the advantage of depth of discharge and cycles. At 50% discharge the projected life cycle is 3600 to 4200 cycles (100% to 50% SOC). At 65% discharged 1800 to 2000 At 80% discharge that drops to 1000 to 1300 cycles, and at 100% discharge 600 to 800 cycles. (These figures from the Firefly website). These are controlled lab discharges, not necessarily in the marine environment--with the abuse that many boaters give batteries. Actually the more you abuse a battery, probably the more sense the Firefly battery makes--since it will fully recover from a 100% state of discharge, something that normal AGM will not do.

Compare with a quality AGM: 50% ~1000 cycles, and 80%~800 cycles, So when you get to the 80% SOD level there is not a whole lot of difference in the longevity.

Lets put this into practical matters. If you are a live aboard and fully cycling your batteries each day (as we did for 4 years), then it really will pay to go with the highest life cycle batteries. However for the average recreational boater who takes at a max a month cruise a year, and a couple of dozen weekends, when he does not fully cycle his batteries even to 50%--then it makes little sense to use the more expensive foam / gel (Firefly) batteries).

The firefly are only made in group 31 currently--and weight is 75#--about the same as my AGM batteries. When put together my 3 group 31 all identical AGM's I figured that I could cycle one or two of them to 80% on occasion and it would be acceptable, since I try and re-charge fully at least once a week. (Normally I'll cycle between 60% SOC to 10% SOC--due to the length it takes to fully top off a battery, which we do when in a marina for overnight.) Otherwise we push charge the group 31 we are running 2 chest refer/freezers in about 2 hours--over an hour of that at 30 amps (watching battery temperature.

Conclusion--for the average C Brat even a lead acid battery is still the best choice of cost vs longevity. (I have some lead acid starting batteries in my RV which are close to 10 years old, and still functioning well) There are many advantages to the Firefly and Lithium batteries-but in my opinion are not worth the increased cost, mainly because of the way we use our boats.

The reality is that 95% of boat batteries die of neglect, (and this may be a good reason to get the Firefly) rather than excessive cycling. How many C Brats cycle their batteries 80% SOC even 20 times a year?

Again--Greg, thank for pointing out the advantages of the carbon foam/lead battery.
 
I use a traditional flooded lead acid (not AGM) deep cycle Costco battery whenever I have the chance. The start batteries on Aurelia, plus the starting battery on our Lund and Sorenson are traditional flooded types.

I turn my gaze to AGM or other types when my use is interior space and venting is a concern, or the mounting position is non-standard. I know the rear compartments on the 22s where folks commonly put batteries is a snug area and think the mounting flexibility of an AGM allows for more sizing/positioning options if that would be helpful.

The basic Flooded batteries are cost effective for many applications. With the original poster running a 115hp outboard, the cranking amps needed for consistent starting may dictate the need for a starting type battery as opposed to a dual purpose or deep cycle model and I would recommend he consider that detail.

I also hope the Firefly brand has more than one size available the next time I am shopping for power

Greg
 
One more note.

I did find some owner references to the Merc 115 four stroke needing a high cranking start battery for reliable starts and people experiencing problems when using a normal size dual purpose type with that motor.

The real concern is how big of a dual purpose or deep cycle (with their lower cranking amps) would it take to start that motor well enough, and how much larger and heavier is that unit when compared with a group 24 or 34 starting model.

If you run your accessory power loads to your house battery and only use the starting side for starting, I would go with the smallest, hardest cranking "starting" unit readily available and save the cost, space, and weight.

Why do Bob and I like batteries so much? I think we both like self sufficiency with predictability and batteries are a very tangible embodiment of those characteristics.

Greg
 
A little more info. I do make several outings a year, of 1 or 2 weeks on the boat. While at home I tend to keep it on the charger. On the water at night I'll possibly run a Cpap machine (without humidifier) off a 100 Watt inverter, the Wabasto Heater, an Anchor LED light, one or two 12 volt fans, and for a few hours, a cabin LED light. I've never seen my battery voltage below 11.9 vts in the morning with the heater running, or 12.2 with it off. Early in the evening, it seems like the voltage is at 12.4 or so. My current batteries are 5 years old, Diehard Marine, that still seem to be doing good, but thinking about Alaska next summer and I'm doing some preventative maintenance. (I use my house battery at night, a Sears DieHard Marine Deep Cycle 600CCA M3 27M. My current starting battery is a DieHard Marine Starting 500 CCA M1 24M. Both have done a good job for me. I'd likely replace with the same thing, or find a dual pupose hybrid that is good both as deep cycle and starting. Maybe just see what Walmart or Farm & Fleet has. I like the idea of AGM as it removes the need for monitoring the acid level, but I don't want to make any changes to my charging equipment...) Colby
 
Your new mastervolt charger and outboards will be able to handle the charging of either type you choose so I would not worry to much about your charging setup. It sounds like you are using most if not all of your house capacity overnight at present. Do you have any reason to think you will use more
or less power on the Alaska trip?

More heating?
Shorter nights?
Running time vs. anchored time?
Less fan use?

Things to consider,

Greg
 
westward":blkdeg9k said:
I have a couple of interstate marine AGM batteries, 3 years on with no problems. I desired AGM because I moved my battery bank forward/enclosed for weight distribution which worked very well. These are very robust, with heavy duty posts and cases. Also totally sealed and can be mounted in any position or without ventilation. They cost ~ 175 each new.
Click to expand...

One word of caution- AGM batteries are actually flooded lead acid batteries but use gel and can thus use closer spaced plates. They are not totally sealed (extremely low outgassing but still possible in certain charging conditions) and therefore cannot be mounted upside down. Close to vertically upside down, but not straight up and down.

PS- I think AGM's are great, use them in all my vehicles, but look forward to using safe and reasonably priced Lithium Ion batteries in the near future
 
Agree that for most folks the Lead acid are fine and the best buy.. When we were cruising full time, and crossing oceans, our 1200 amp hour battery bank was entirely of lead acid deep cycle golf carts--and they were still in good shape after over 5 years of use daily use.

I made a mistake when I put "Normally I'll cycle between 60% SOC to 10% SOC-"

That should have been normally cycle between 60% SOC to 90% SOC.
 
Hi Greg, thanks for the info on the starting battery. No, I don't see anymore amperage draw on the batteries at night. I think I'm pretty maxed out now, even though with the LED's and low amperage fans, not much is being drawn. I'd say my heaviest draw is from the Cpap on the 100Watt inverter (the inverter gets warm, so I know it's probably providing somewhere near it's limit), and the Wabasto Heater when the glow plug is on. My routine is to usually start the outboard on the Starting battery, then run the battery switch to both batteries to recharge both. If I'm going to be running long, I'll just recharge one battery at a time. Then I leave the switch to the starting battery until turning in for the night, at which time I switch to my house battery. Colby
 
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