Solar Battery is Toast?

annaanna Registered Users Posts: 1

I am very new to solar.  I own a Sprinter van and for the past 2 winters removed my AGM battery for the winter.  I recently learned I should have had it on a charge control maintainer so I did that for the past month.  I just hooked the battery back up to my system and it shows a charge of 14.2.  As soon as I run my fridge for couple hours it drains to 12.4 (danger level).  Is my battery toast?

If so, do I buy Vteck or Lifeline?  I currently have Vteck.


  • BB.BB. Super Moderators, Administrators Posts: 28,140 admin
    It does depend on the size (Amp*Hour Rating of your battery(ies)) and the size of your load. Smaller battery + larger loads--Yes, batteries get "stressed".

    It is not uncommon for a lead acid battery to drop a few 0.1 volts (12.7-12.8 volts fully charged and "resting") and come back up after a bit (and especially after the loads are turned off).

    Pulling a lead acid battery down to ~11.5 volts under a good size load is not the "worst" thing in the world.

    Resting voltage of 12.3-12.4 volts is typical for 50% discharge state (cannot measure specific gravity of electrolyte for sealed AGM/GEL/VRLA batteries).

    AGM batteries, if stored in a cool place (after being fully charged) can sit for 3-6 months without charging (a good quality AGM float charger is good--Or charging one day a month for non-float chargers).

    Knowing more about your loads (a typical AC fridge draws ~120 Watts @ 120 VAC or I=P/V=120 Watts/12 volts=10 amps @ 12v volts (real rough calculation).

    If you have a 100 AH @12 volt battery, then 10 Amp discharge will draw 50 AH (or 50% state of charge) after 10 hours.

    Details matter here (using some sort of meter(s) to measure load and charging currents, etc.).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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