Batteries Overcharging Badly

[davidbrady]

Mike,

These problems are notoriously difficult to debug remotely and even harder when the coach isn't in your possession; nonetheless, I have a few questions:

1) What kind of house and chassis batteries did you install?

2) Which ones are off-gassing H2S?

3) What's your Xantrex RC7 charging configuration?

4) I assume you know about the 'aux-batt' switch on the dash and it's operation?

5) Have you checked the status and diagnostic LED's on the Xantrex chargers.

6) Are your Xantrex Battery Temperature Sensors adhered to the side of you house batteries?

I'm siding with your mechanic and his inclination that the batteries are the problem since you see this issue with both alternator charging and Xantrex charging. As a precaution, and given how much you've already spent, I'd replace the other 2 chassis 4D batteries. If 4 were weak the other 2 can't be far behind.

I'm suspecting a faulty cell or shorted cell such that the remaining cells are seeing excessive voltage. A simple test is to disconnect all batteries, let them sit for four hours and then measure their open circuit voltage; they should read 13.0V.

Lifeline provides these guidelines for load testing their AGM batteries:
1. Stabilize the battery at 68-86 deg F for at least 24 hours.
2. Bring the battery to full charge.
3. Discharge the battery at a constant current of 25 amperes until the voltage falls to 10.5 volts. Record the time in minutes.
4. Compare the measured discharge time to the published 25A rating.
5. If the battery delivers less than 80% of the rated capacity the conditioning procedure should be attempted an the battery should be retested.
6. If the battery delivers less than 50% of its rated capacity it should be replaced.