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donaldn01 asked

BMV 712 False reading after dead batteries?

I recently had my RV in for service. It was there for about 18 days. I must have left the water pump on by mistake. When I went to pick the RV up the batteries were completely dead. The "phantom load" (Propane detector, radio, etc.) should not have depleted 180 Ah of batteries. My guess is the water pump kept cycling till the batteries were dead. When I hooked up to shore power after about 15 minutes the BMV said State of Charge was 100%. I know this can not be correct. Is it possible to get a false reading on "dead" batteries, or are my batteries "dead" and no longer accepting a charge? I know you are not suppose to let Lead Acid batteries go below 50%. Can a 1 time complete discharge kill the batteries. Any info and tips would be appreciated.

BMV Battery Monitor
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Kevin Windrem answered ·

There is a configuration item that instructs the BMV to reset to 100% on power up. If you turn this off, it should retain the last known SOC on power up.

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donaldn01 answered ·

The set to 100% on start up is off. When powered up the state of charge is "unknown" or just dashes, which is correct as it does not know the state of charge. It only takes a few minutes and then it jumps to 100%. I know this can not be as the batteries we completely drained. When I disconnect the shore power, the battery voltage is only 11.6ish volts.

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Kevin Windrem answered ·

If the battery voltage reaches the float voltage and the charging current drops to near zero, the BMV will reset the SOC to 100%. This might be happening if the batteries have disconnected due to the drained condition, or if they are damaged and won't take a charge.

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donaldn01 answered ·

Update: The charger I use to trickle charge the batteries durring the winter has a " reconditioning" feature so I ran that on both batteries and then charged them. Put them on the camper, set the state of charge to 100%, and left them for a couple days. The draw on them was about 0.2A, which is normal for radio, CO2 det. etc. Last time I looked the state of charge was 95%, but the voltage was 12.32v. According to standard voltage charts this would indicate the batteries are at 70%. Does this discrepancy indicate the batteries are bad?

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