Question about Battery Water Usage

I'm really new at this solar stuff and sort of learning on the fly. I am very interested in solar for RV's. I have two 115 volt PV panels on my RV roof and two 12 volt batteries and two 6 volt batteries. Controller is inside RV and batteries are in outside compartments. My controller is a Sunsaver 20 amp. Problem I have is the 6 volt batteries boil and I have to add distilled water every month. Can anyone explain what is happening that causes this? and what can be done about it? Thanks,


  • BB.BB. Super Moderators, Administrators Posts: 30,526 admin
    Re: Expanding Forums?

    Having to add "reasonable" amounts of distilled water every month (especially during the summer) is normal. If you are not adding any water, then the batteries are probably undercharged.

    If your are just topping off the cells, instead of down to the plates--things are probably fine. You can also look at these "water miser" caps--they can also help keep the water/acid in the battery.

    Using a solar charge controller with a remote battery temperature sensor will help to a degree (depends on temperature of battery vs charge controller).

    Also, it is possible that you are overcharging your batteries... Getting a DVM (digital voltmeter--should be accurate to 12.xx readings, at least) and checking your battery voltages (at the terminals) as they are charging will quickly tell you if there is a problem.

    Lastly, if you have a hydrometer that shows your batteries are fully charged but the controller is still outputting "high" currents to the battery bank--then you may have a bad (or miss-configured) charge controller.

    You probably have multiple charging controllers in your RV (solar, AC shore power, RV Alternator, RV aux generator, perhaps even a trickle charger for off-season storage)--and any of these could be causing your (possible) overcharging.

    It will require that you check each device/system individually (with the others turned off) to find the problem (if there is a problem).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Expanding Forums?

    i have to ask what configuration those batteries are in for if you are not putting the 2 6v batteries in series with each other and all batteries are paralleled then the voltage is all wrong and intermixed and it will boil the 6v batteries and not charge the 12v batteries. those 12v batteries will also become part of the problem as they will drain into the 6v batteries too. i also find that intermixing different batteries can be dissastrous too even if all of the same voltage type. small differences in the batteries will cause problems in the charge/discharge curves making some batteries possibly work all that much harder than others leading to shorter lifespans. try charging the 2 12v batteries seperate for a day or 2 and then charge the 2 6v batteries seperately from the 12v batteries and make sure they are in series to make those 2 6v batteries into a 12v battery bank after you confirm general things such as electrolyte levels, individual battery voltages, specific gravities, and any other maintenence items to all be proper. let us know what you find.
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