I recently purchased a used C-Dory 25' cruiser and I am needing to replace the batteries. My question is what group size is reccomended or is there that big of a difference between the 27 and 31. Also, i am going with the AGM versus the flooded cell if that has any impact on the group size. Any help is greatly appreciated.
Battery group size
- Thread starter Aubbrey
- Start date
Robert H. Wilkinson
New member
What are your current batteries? Several variables. What are your house needs? What size engine? What cranking amps are required? How will they be recharged? Bigger is not always better if charging capacity is minimal. Colder climates also play a role requiring higher cranking amps.
I recommend a dedicated start battery and dedicated deep cycle for house.
Also marine rated has better support between plates for vibration.
Rob
I recommend a dedicated start battery and dedicated deep cycle for house.
Also marine rated has better support between plates for vibration.
Rob
Definitely go with the AGM for boat use. I have yet to find a "flooded" lead acid battery that does not leak a little in heavy seas. My first electric boat (29 years ago) had 12 flooded golf cart batteries, and I tried all kinds of tops/plugs. All of them ended up leaking to some degree, and the batteries needed to be topped off with distilled water regularly.
As already mentioned you should have a "starting" battery for your outboard and a "deep cycle" battery for your house load. The latter will last much longer when you need to discharge it below about 80% SOC (state of charge). Also note that batteries listed as both starting and deep cycle are a compromise and have all of the "negative" aspects of each type without being as good as each type separately.
This is what I found on Google [Group 31 batteries generally offer a higher cold cranking amp (CCA) rating compared to Group 27 batteries, meaning they are better at starting engines in cold weather. Group 31 batteries typically have a CCA range between 700-1150, while Group 27 batteries range from 600-1000]
As already mentioned you should have a "starting" battery for your outboard and a "deep cycle" battery for your house load. The latter will last much longer when you need to discharge it below about 80% SOC (state of charge). Also note that batteries listed as both starting and deep cycle are a compromise and have all of the "negative" aspects of each type without being as good as each type separately.
This is what I found on Google [Group 31 batteries generally offer a higher cold cranking amp (CCA) rating compared to Group 27 batteries, meaning they are better at starting engines in cold weather. Group 31 batteries typically have a CCA range between 700-1150, while Group 27 batteries range from 600-1000]
gulfcoast john
New member
Congratulations on your new ride, great boat!
The ‘Group’ number is just an external case size dimension. Agree with Rob that the charger should also be adequate. My TC255 came with three Group 31 batteries, and a puny little Guest 10/5/5 charger.
If you anchor out a lot, you may want more battery power. If you find a deep-cycle battery that also meets ALL the specs for the engine (per your engine manual) you can ‘combine’ them for extra power on the hook. You don’t want to use a ‘starting’ battery for that, they are designed for massive amps out but only for way less than one minute. If you have the room, I’d suggest two Group 31 until you decide how you like to use your boat. The fridge compressor is the biggest overnight 12v hog on the boat, and many owners can get only one or two nights without recharging (with the engine in fast neutral or generator or solar panel). If you plan to have radar, rooftop AC, bicycles and kayaks up there you may not have room left for a solar panel.
So much depends on how you plan to use your boat…that makes it difficult to generalize too much. Certainly Lithium will become the House battery standard (few are rated as ‘start’ batteries yet), but they are not yet a ‘drop in’ replacement for your old batteries, and you may not want to pay an expert for that expertise after you just bought a CD-25.
Don’t fret…you’ll figure out what you NEED vs what you WANT just like the rest of us. PM or call if I can help, we’re on the Loop at the top of Michigan in SCA in the rain and I’m bored.
Safe Travels!
John
The ‘Group’ number is just an external case size dimension. Agree with Rob that the charger should also be adequate. My TC255 came with three Group 31 batteries, and a puny little Guest 10/5/5 charger.
If you anchor out a lot, you may want more battery power. If you find a deep-cycle battery that also meets ALL the specs for the engine (per your engine manual) you can ‘combine’ them for extra power on the hook. You don’t want to use a ‘starting’ battery for that, they are designed for massive amps out but only for way less than one minute. If you have the room, I’d suggest two Group 31 until you decide how you like to use your boat. The fridge compressor is the biggest overnight 12v hog on the boat, and many owners can get only one or two nights without recharging (with the engine in fast neutral or generator or solar panel). If you plan to have radar, rooftop AC, bicycles and kayaks up there you may not have room left for a solar panel.
So much depends on how you plan to use your boat…that makes it difficult to generalize too much. Certainly Lithium will become the House battery standard (few are rated as ‘start’ batteries yet), but they are not yet a ‘drop in’ replacement for your old batteries, and you may not want to pay an expert for that expertise after you just bought a CD-25.
Don’t fret…you’ll figure out what you NEED vs what you WANT just like the rest of us. PM or call if I can help, we’re on the Loop at the top of Michigan in SCA in the rain and I’m bored.
Safe Travels!
John
I have always switched to group 31 for the house bank. I do run with chest freezers/refers, so have that extra load. The group 31's fit between the 22's fuel tanks. On the last 25, I also had two 100 amp hour LiFePO4 batteries. These have amost twice the "power" of the group 27 (if not more power). You do have to have a DC To DC charger for the Li batteries.
If I was outfitting a 25 currently, I would go with the Li. There are some of the LiFePO4 which are actually cheaper than the AGMs now. Check Will Prowse's videos on the best Li batteries.
If I was outfitting a 25 currently, I would go with the Li. There are some of the LiFePO4 which are actually cheaper than the AGMs now. Check Will Prowse's videos on the best Li batteries.
colbysmith
Active member
FWIW, on my 25, I run one group 24 or group 27 marine starting regular flooded wet cell battery. Then I have two group 31 AGM's in parallel for my house batteries. I was using two group 29 flooded wet cell batteries up until a month ago. The Fwc have worked fine for me in the past, but I think Walmart got a little cheaper in the make of their batteries and I was having an issue maintaining above 12 vts in them over night (12+hours). Also, I run a Cpap (without humidifier), refrigerator, portable freezer, webasto heater, and some fans and LED lights. The frig and freezer pull 3 amps each when they are running. The Webasto heater draws 8 amps for a short period of time when it is firing up or shutting down. I don't think my cpap draws more than an amp or two. And LED's are neglegible. AGM's cost about twice what flooded cell do. And the Lifepros I've heard about cost close to $1000. FLooded cell have been around for ever and unless you are running a lot of load, will probably do fine for the cost. The group size comes down to where your battery is stored and how big is the opening to get it there. For a house battery, I would go to the biggest size you can fit, realizing the bigger the battery, the more amphours and the longer it will take to recharge.
My experience is that most of the chest freezers and refrigeratos, draw is closer to 5 to 5.5 amps when running. The overall draw is possibly close to 3 amp over all. 24 hour run of either of these is about 60 amp hour--I have never seen 36 amp hours use which Colby suggests his get, I have been using these chest type units for almost 50 years not. First was in a Van Conversion Marie and I did in 1977. That Norcold chest lasted for over 20 years.
You can currently guy LiFePO4 100 amp batteries for about $250. I have four of them in my "household" back up system. They seem to be working well. Any good battery system needs monitoring. I have seen other brands for as low as $140 on Amazon currently.
Even if you use FLA or AGM, I advise the Victron 702, or for 1/4 the price a chinese copy (which I have also been using for several years and seems to work as well.). For an inverter, I would recommend Victron.
Renology 100 amp hour: $275, (I have been using one of these in my cars for everyday freezer work--bringing frozen food home from the grocery store)
SOK 100 amp hours batteries for $299.
You can currently guy LiFePO4 100 amp batteries for about $250. I have four of them in my "household" back up system. They seem to be working well. Any good battery system needs monitoring. I have seen other brands for as low as $140 on Amazon currently.
Even if you use FLA or AGM, I advise the Victron 702, or for 1/4 the price a chinese copy (which I have also been using for several years and seems to work as well.). For an inverter, I would recommend Victron.
Renology 100 amp hour: $275, (I have been using one of these in my cars for everyday freezer work--bringing frozen food home from the grocery store)
SOK 100 amp hours batteries for $299.
Most of the chest refers/freezers use the same Danfoss compressor, or a Swing Motor. Danfoss comes in two sizes: BD35F and BD50F, Over half of all chest units use the Secop/Danfoss compressor, another common compressor is the
Sawafuji swing motor compressor. Between the two, of all of the units I owned (at least a dozen thru the years) used one of these two compressors.
For the most part they all have the same size compressor: the BD50 by Danfoss. The amount of current draw depends on the speed of the compressor. The Danfoss is "listed" as 2.2. to 3.8 amps. This is from the Wabasto 35 quart up to a 90 liter double chest type (Whynter 90 quart ). I had for a couple of years. (That was sourced from another C brat who had envisioned putting it down below in the Cabin of his C Dory 25.) That 90 liter unit had the same Danfoss 50 compressor that several units which were 50 quart sized units. Even the specifications for this unit says: "12V – 5.5 Amps" max current draw for the single Danfoss 50 compressor. This matches what I observed with the unit running on my boat. I always monitor individual appliances before beginning trips--use freezing water as an end point.
Yes the web sites say "2.2 to 3.8" amps draw, my tests averaged more than that--closer to 5 amps. I measured run times for each unit, as well as current draw under "normal" conditions when I was considering how much LiFePO4 battery amperage I would need in the C Dory 25 running two 50 quart chest freezers/refer units. I ran these tests over a number of weeks to smooth out flectations. We measured "instant draw" to total current over 24 hours.
My numbers are based on a number of observations over a peroid of many years. I also want to figure for "worst case" when looking at battery draw. A couple of other comments about the Chest feezer/refer combos. These are very poorly insulated in comparison to a Yeti ice chests, or units I have built in boats, with 6" of closed cell foam surrounding the entire unit--sides top and bottom. So these have 3/4" or so--some a little more. The motors are under and next to part of the unit, and of course produce a lot of heat, along with the radiator part of the unit. These ares should be ventillation with a fan to blow the heat out of the area where these chests reside. For example in the refrigerator chest in our last 25 was on slides under the navigator's seat. When all of the way back and locked in, there was a fan blowing thru this area, controlled by a snap disc thermostat set at 100*, so there was basically forced ventillation, with an opening on the other side of the area (under the navigators feet). I had a "2" more insullation "jacket" for the top and sides of these chest units when they were in the cockpit--of course it left the ventillation ports open, or had a fan similar to what was used under the seat in the cabin. For freezer units we kept in the cockpit, we had an old white thick bedspread cut up
to make a loose outside cover for the freezer unit. That was kept damp or wet, to give additional cooling effect when exposed to ambient heat--for example at Lake Powell. Or cruising the rivers of N. America.
The reason that realistic utility draw is important is that many of the C Dorys have only 2 batteries. You never want to wake up in the moring and find out both batteries are dead. No way to start the outboard--unless some of you can hand start a 200 hp Suzuki? In our last 25 C Dory I had 2 house, group 31'a plus the group 24 engine start, AND a 200 amp hour (180 amp hour usable) LiFePO4 battery bank for the refrigeration, and inverter which ran a microwave and an induction burner. (Burner heats the cabin less than a fueled stove top in Florida's heat..)
Here is a web site on this issue from a van RV web site.. Follow some of the sub links. We may differ in how much current draw there is by type of compressor (and amount in run in 24 hours, related to size of unit in quarts or liter volume. Keep your batteries charged!
Sawafuji swing motor compressor. Between the two, of all of the units I owned (at least a dozen thru the years) used one of these two compressors.
For the most part they all have the same size compressor: the BD50 by Danfoss. The amount of current draw depends on the speed of the compressor. The Danfoss is "listed" as 2.2. to 3.8 amps. This is from the Wabasto 35 quart up to a 90 liter double chest type (Whynter 90 quart ). I had for a couple of years. (That was sourced from another C brat who had envisioned putting it down below in the Cabin of his C Dory 25.) That 90 liter unit had the same Danfoss 50 compressor that several units which were 50 quart sized units. Even the specifications for this unit says: "12V – 5.5 Amps" max current draw for the single Danfoss 50 compressor. This matches what I observed with the unit running on my boat. I always monitor individual appliances before beginning trips--use freezing water as an end point.
Yes the web sites say "2.2 to 3.8" amps draw, my tests averaged more than that--closer to 5 amps. I measured run times for each unit, as well as current draw under "normal" conditions when I was considering how much LiFePO4 battery amperage I would need in the C Dory 25 running two 50 quart chest freezers/refer units. I ran these tests over a number of weeks to smooth out flectations. We measured "instant draw" to total current over 24 hours.
My numbers are based on a number of observations over a peroid of many years. I also want to figure for "worst case" when looking at battery draw. A couple of other comments about the Chest feezer/refer combos. These are very poorly insulated in comparison to a Yeti ice chests, or units I have built in boats, with 6" of closed cell foam surrounding the entire unit--sides top and bottom. So these have 3/4" or so--some a little more. The motors are under and next to part of the unit, and of course produce a lot of heat, along with the radiator part of the unit. These ares should be ventillation with a fan to blow the heat out of the area where these chests reside. For example in the refrigerator chest in our last 25 was on slides under the navigator's seat. When all of the way back and locked in, there was a fan blowing thru this area, controlled by a snap disc thermostat set at 100*, so there was basically forced ventillation, with an opening on the other side of the area (under the navigators feet). I had a "2" more insullation "jacket" for the top and sides of these chest units when they were in the cockpit--of course it left the ventillation ports open, or had a fan similar to what was used under the seat in the cabin. For freezer units we kept in the cockpit, we had an old white thick bedspread cut up
to make a loose outside cover for the freezer unit. That was kept damp or wet, to give additional cooling effect when exposed to ambient heat--for example at Lake Powell. Or cruising the rivers of N. America.
The reason that realistic utility draw is important is that many of the C Dorys have only 2 batteries. You never want to wake up in the moring and find out both batteries are dead. No way to start the outboard--unless some of you can hand start a 200 hp Suzuki? In our last 25 C Dory I had 2 house, group 31'a plus the group 24 engine start, AND a 200 amp hour (180 amp hour usable) LiFePO4 battery bank for the refrigeration, and inverter which ran a microwave and an induction burner. (Burner heats the cabin less than a fueled stove top in Florida's heat..)
Here is a web site on this issue from a van RV web site.. Follow some of the sub links. We may differ in how much current draw there is by type of compressor (and amount in run in 24 hours, related to size of unit in quarts or liter volume. Keep your batteries charged!
Robert H. Wilkinson
New member
Another factor to consider when calculating amps is the voltage. To calculate an appliances specific amp draw the specific voltage should also be noted while recording test results.
Rob
Rob