Adding batteries

[rajjes]

I have been given 2 X 100Ah sealed lead acid batteries from decommissioned UPS’s which are still in great shape and I’m considering adding them to the boat.

Currently I have 2 X 110 Ah for the domestic bank and 1 X 90 Ah for the starter battery. All batteries are sealed lead acid. Charging is via engine alternator, 80W solar panel on house bank and ‘intelligent’ charger with 2 outputs when on shore power.

Although I am keen on the extra capacity I am not sure how I should proceed on this. The simplest route would be to just add the batteries to the existing house bank but it seems that different age / Ah on the same bank is frowned upon? I am also considering adding the 2 batteries as a separate house bank but not sure how to switch across banks and maintain optimum charging?

Appreciate your views and possible recommendations!

 

[lpdsn]

I have been given 2 X 100Ah sealed lead acid batteries from decommissioned UPS’s which are still in great shape and I’m considering adding them to the boat.

Currently I have 2 X 110 Ah for the domestic bank and 1 X 90 Ah for the starter battery. All batteries are sealed lead acid. Charging is via engine alternator, 80W solar panel on house bank and ‘intelligent’ charger with 2 outputs when on shore power.

Although I am keen on the extra capacity I am not sure how I should proceed on this. The simplest route would be to just add the batteries to the existing house bank but it seems that different age / Ah on the same bank is frowned upon? I am also considering adding the 2 batteries as a separate house bank but not sure how to switch across banks and maintain optimum charging?

Appreciate your views and possible recommendations!

Having two domestic battery banks would be awkward to manage. You can get three output chargers (my shorepower charger is) but the extra expense of that would no doubt eat up most of the savings.

At least at nominal Ah the battery banks aren't that dissimilar. Are the 110Ah batteries in poorer condition, or much better condition? If not you could do it for now and make a four battery bank. If the 110Ah batteries are in much poorer condition, consider replacing them with the 2 X 100Ah batteries.

What about longer term? I presume you'd eventually need to replace all four, so would you be able to fit 4 X 110Ah or 4 X 100Ah?

Bear in mind that when linking four batteries, the order in which you connect the +ves and -ves should lead to equal paths. No doubt someone will be along soon to post the usual diagram, but the different loads on the batteries is surprisingly significant if you don't do it.

 

[William_H]

I think the primary concerns are in housing and clamping down the added batteries. Yes they can be wired in paralllel with existing house batteries. Yes at some time in the future you will have problems with one or more of four batteries dieing first. Ideal set up is a 1,2,both,off switch ( for the new bank and old bank) or better still 3 of these switches.( so you can switch in or out any battery) In practice you can just have removable battery terminals.(or even use those terminals witha switch built in) If you find at any time that charging or discharge voltage seems a bit suspect then try disconnecting each battery one at a time to see if one is dieing and so dragging the others down. Or occasionally just use one battery for discharging but check each one individually. Likewise you might want to ensure each battery alone can start the engine.
While all batteries are good you should get a large recharge rate with a short engine run. ie total AH put in. But still just as hard to fully charge all batteries. good luck olewill