mixing group sizes

i have a group 27 120AH .. can i wire (in series) a group 31 if its also 120AH?

For 80lb minnkota

Thanks for any advice

I'm no authority but from everything I've read batteries should be identical for both age and size. If it were me I'd use them if it's just the size that's the difference. The main thing is that they charge at the same rate so as not to deplete one more than the other.

Battery group sizes only define the physical dimensions of the battery itself. That said, any inequality between the two batteries will compromise the life of both batteries. That can be due to how many charge cycles it's seen previous, how old it is, manufacturer, build quality, how it's been stored etc. When you use one battery that is stronger than another in series, it will constantly try to balance the weaker battery and both batteries will suffer for it. How much is the question. That is why the trolling motor manufacturers will always recommend you use the same exact batteries purchased at the same exact time. It wasn't cheap when I set up my 36v trolling motor: