How far to discharge your Lead Acid RV batteries?
The safe answer is about 50% or to 12.1v.
The first place to start will be your battery manufacturer, they should have similar chart. If they do not have your battery specifications readily available, that could be a sign you have the wrong battery.
So if you have Golf Cart (GC) Deep Cycle batteries or better and your boondocking in the shade, rain, clouds or you don’t want to run the generator. This Lifeline chart shows the direct relationship between State of Charge (SOC) and expected life cycles in the laboratory and your wondering what your results may be. Now if I had a crystal ball, I wouldn’t be writing about batteries. I can tell you that you will NEVER reach the life cycles in the real world that someone got in a lab with constant temps and constant charging! I hope to get about ½ the life cycles that my battery got in the lab. All of my research over the years says that everybody has had different experiences. It appears big factors would be temperature, length of time the battery spends discharged and the amount of charge applied to the bulk stage.
Temperature is something that we dont have alot of control over. I installed my battery bank in the living quarters of my RV and they have less of a temperature swing than being mounted in the black box on the tongue. It is very important to have temperature compensation programed into your charger. If you dont you could be overcharging and undercharging the batteries on the same week!
It is recommended to do a capacity test on your system every year. With GC batteries this will require you to discharge your battery to 0% SOC or 10.5 volts at a rate of the 20hr rate. This is OK to do once a year and recharge right away. This is the only way to know what your actual capacity. The sticker on your battery is not a tested AH! If you believe you have 100AH and you use 75AH your SOC is believed to be 25%. If your actual capacity is 80AH you just damaged your battery.
I typically have my batteries around 75% SOC before charging. I have had them at 20% SOC once. Sometimes I get caught without sun on the panels for several days. If I get the battery below 40% I will actually charge with multiple sources to increase the charging amps if available to help burn off any sulfation on the plates. The faster you can get out of the deeper discharges the happier your batteries will be.
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