One new battery or three?

[lumphammer]

My 12 volt setup consists of 2 x 120Ah sealed lead acid for the domestic and a 55 Ah for engine starting. Batteries are about 5 years old and appear to be still holding their charge.

I've found the space for an additional battery on the domestic circuit, which is big enough to allow me to fit a larger physical size (higher capacity battery) than the current ones.

My questions are : -
1) What would be downside to going to a higher capacity for one battery?
2) I know the battery bank should consist of batteries the same age and size, but I'm loath to replace two batteries that seem to be working OK. Should I budget for replacing all three?

 

[No Regrets]

I have a total of five batteries of varying ages and sizes, and have no issues at all.

They are in two banks, one of 2X100A/h and one 110A/h and the second consisting of one 100A/h and one 70a/h.

I was a bit circumspect, but have a 20A/h Sterling charger which services them quite pleasantly, and no excess Water use, in fact virtually none as I only top up once a year, despite regular checks.

 

[William_H]

Yes by all means add another domestic battery in parallel with old ones. However when and if you seem to get capacity and volt drop problems you will need to isolate each battery to find the bad one. Indeed occasional disconnect all but one battery after fully charging and see how long it last say running fridge or some similar discharge. Then compare to the other 2 batteries each in the same way. All to ensure that they all continue to pull their weight. olewill