Group 34 and group 31 in two battery setup?

[WiskyDan]

I bought two group 34 deep cycle AGM batteries a couple years ago and the house battery may need to be replaced - it’s having trouble holding a charge. I have some more investigating to do this weekend but if I have to replace it I’m thinking of going with a group 31 so that I have more capacity. Does using two different group sizes in the same boat cause any issues for the stator when they’re recharging?

 

[FSH 210 Sport]

I bought two group 34 deep cycle AGM batteries a couple years ago and the house battery may need to be replaced - it’s having trouble holding a charge. I have some more investigating to do this weekend but if I have to replace it I’m thinking of going with a group 31 so that I have more capacity. Does using two different group sizes in the same boat cause any issues for the stator when they’re recharging?

The different group sizes shouldn’t be a problem.

Does your boat have the OEM BEP Marine battery switch with a DVSR ? Do you have an onboard charger that you plug in when not on the water?

Also, did you mean you bought two group 24 batteries two years ago and not group 34?

 

[WiskyDan]

Thank you for the reply. I do have the switch with the DVR and they are group 34 - Odyssey (Extreme )brand. I got a good deal on them but they are only 68Ah and I’d like to get something closer to 100Ah. If I do have to replace the group 31 size looks like the best option. I’ll have to swap out the battery tray but that’s minor.

 

[FSH 210 Sport]

Thank you for the reply. I do have the switch with the DVR And they are group 34 - Odyssey (Extreme )brand. I got a good deal on them but they are only 68Ah and I’d like to get something closer to 100Ah. If I do have to replace the group 31 size looks like the best option. I’ll have to swap out the battery tray but that’s minor.

You are welcome! Huh, I thought group 34’s were bigger than 31’s… as Kyle would say, “You know, I learned something today”.

Yeah a group 31 should be right at 105 Ah’s I think, a group 27 is usually around 90.

To get the most out of your house battery, you might consider hooking up the dvsr hot to an ignition hot so that batteries separate as soon as you turn off the engines. This will avoid the batteries falling to 12.7 volts together before the DVSR separates them.

Also, I suggest installing a Victron smart shunt so you can keep track of, Ah’s used, Watt hours used, voltage, instantaneous amps both in and out of the battery, and voltage of the start battery.

 

[WiskyDan]

Thank you for the tips!!!

Group 34’s have the same dimensions as group 24’s (the batteries that came with the boat) so I didn’t have to swap out battery trays.

 

[FSH 210 Sport]

When I put my 100 Ah LiFePO4 battery in to replace the group 24 house I used a piece of cutting board to span the gap of the OEM recess and screwed it down and attached the strap to this cutting board. That has worked out great for me.. now I can run my live well system all day long, along with my fish finder and the OEM stereo and never get low on battery power. Going to the 100Ah AGM will give you a big boost in supply for your day on the water.

 

[MrBubbaGump]

When I put my 100 Ah LiFePO4 battery in to replace the group 24 house I used a piece of cutting board to span the gap of the OEM recess and screwed it down and attached the strap to this cutting board. That has worked out great for me.. now I can run my live well system all day long, along with my fish finder and the OEM stereo and never get low on battery power. Going to the 100Ah AGM will give you a big boost in supply for your day on the water.

How long of screws did you use to screw the cutting board down... I Just ordered a 3rd battery that I am going to isolate from the rest of the boat (other than grounding to each other) for my amps. So I was planning on ordering a piece of 1/4 inch star board large enough to hold all three batteries over the OEM recess.

 

[FSH 210 Sport]

How long of screws did you use to screw the cutting board down... I Just ordered a 3rd battery that I am going to isolate from the rest of the boat (other than grounding to each other) for my amps. So I was planning on ordering a piece of 1/4 inch star board large enough to hold all three batteries over the OEM recess.

I don’t recall how long the screws were…as I said I got a cutting board from Sams that was made out of slippery white shit as they like to say, Id think that would be plenty strong but you’d have to use one piece for each battery. It leaves a nice little cubby to put stuff in underneath as well. The oem recess is part of the liner, it’s maybe 1/4” thick?, and I don’t think there is anything under it, I know I checkedby carefully drilling a pilot hole then saw hoe deep the drill bit would go in while the drill was off.