Topping off house bank, only 3 of 4 batteries needed water...

[Beach View]

Hello CF,

I hope you can answer a couple of questions about my house bank.

It consists of 4 X 125 Ah FLA batteries in parallel, they are two years old, seem to have no problems so far. See the picture for the setup.

I just topped off the batteries with distilled water--the last time I topped them off was in March, and I’m in Southern Italy. During this time the boat has been on shore power/battery charger for 3 months (thanks COVID…) and sailed weekly for 2 months (mix of battery charger, engine, and generator). I found three of the batteries (first three in a row, from left to right, 18 cells total) needed a total of just under 2 liters to top off (all of the plates were still under water), and one battery (last one on the right, 6 cells) did not need any water at all. I haven’t had a chance to check the specific gravity of all the cells, which will probably tell me something….

Here are my questions:

1. What’s the deal with 3 batteries needing water and one being full?
2. I have a battery charger (separate from the boat’s chargers) that has an equalizing function. Can I equalize all four batteries at once while they are in parallel? Should I equalize the batteries separately? Should I equalize the batteries separately, then do it again while they are in parallel?

Thanks in advance for your help--I know there are electrical gurus out there, I hope to get there eventually…

Bill