By Mark Polk
RV EDUCATION 101®
Never let a 12-volt battery discharge below 12 volts, or a 6-volt battery discharge below 6 volts. That might sound funny, but a fully charged 12-volt battery is actually 12.7 volts and a fully charged 6-volt battery is 6.37 volts. When a battery reads 12 volts, it is at or below a 40% state of charge.
You can measure the voltage using a digital voltmeter. Measuring the voltage gives you a quick picture of the battery’s depth-of-discharge, so you know when the battery needs to be recharged.
Set the voltmeter on DC voltage, and place the red lead on the positive terminal and the black lead on the negative terminal to read battery voltage. Charge any 12-volt battery that reads 12.5 or less volts.
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Mark Polk’s tech tips are posted every Saturday in the RV Travel Newsletter and every Wednesday on the RV Daily Tips Newsletter.
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It is sad that there are still those out there that continue to spread false statements about depth of discharge for flooded batteries (the 50% rule) and now this! Without a battery monitor that counts amps in and out a voltage reading is a guess at best as to the state of charge. Are the batteries at rest, are they being lightly discharged, or are they running a furnace? Each one will give a vastly different voltage but each one will be at the same state of charge. At rest a flooded battery measuring 12v is about 50% SOC and taking it down to 20%, 30%, or 40% SOC is not a death sentence, contrary to popular myths.