Dead Batteries

Dead Batteries

by Gordon (Baton Rouge, LA)

Question: I have a 1998 Gulfstream Scenic Cruiser that works fine when plugged in to a power source and also works fine when the generator is running. But when I turn off the generator, the power panel shows that the batteries are dead and nothing works including restarting the generator.

If it is plugged into a power source when the generator is shut off, the power panel shows the same but in a short while (20-30 minutes) it shows the batteries are good again. Please help.

Answer: You may have multiple problems so let’s address them one at a time.


A badly sulfated battery will appear to recharge within 20 – 30 minutes. This means that it is only accepting a surface charge. That is why your battery(s) appear to recharge in such a short period. If my batteries are at half capacity (about 12.2 volts), it usually takes anywhere from two to four hours to reach a float charge. By the way, we had two deep cycle AGM 8D batteries that started to do this and eventually had to replace them.

Diagnosing the batteries

Start by cleaning your battery terminals, and check that the battery connections are tight. With the generator and shore power off, take a voltmeter and read your voltage directly from your battery terminals.

If the voltage is under 11.8 volts, your batteries may not be salvageable. Take your batteries to a trustworthy battery shop to have them load tested. If they are the lead acid type, also have them check each cell with a hydrometer to see if there is a bad cell. You could do this yourself with the proper equipment, but it is easier to have a trusted professional do this.

If the voltage is over 12 Volts or better than there is hope to save the batteries. You may have to equalize the batteries several times to clear the sulfated crystals from the battery plates. Caution: if you are using AGM batteries read your battery manufacturers’ recommendation on equalization, since they may recommend that you do not equalize an AGM battery.

Put a load on the batteries (no shore or generator power) and wait till the voltage drops to about 12.2 Volts. Plug the RV back into shore power and see how long the battery(s) takes to recharge from your shore power. If it now takes hours then you have successfully eliminated the sulfated battery problem.

Generator system:

When your generator is operating, it should be charging your batteries. From the information given, it appears that the generator is producing power but the power is not getting to the charging circuit.

Diagnosing the Generator System:

If you have not done so, check the circuit breakers on the generator and reset them. While you are at the generator, take a voltage and amperage reading while the generator is operating and shore power is off. You should see 120 Volts. See your generator specs for proper amperage output.

Next, start by checking connections between the generator and the inverter/charger or converter. Look for a blown fuse, loose or broken wires. If you have not already done so, clean your battery terminals and check that the battery connections are tight.

Go to the battery compartment and with the generator and shore power off, take a voltmeter and read your voltage directly from your battery terminals. As previously stated, the voltage on a good battery should be above 11.8 Volts.

With the shore power off, have someone start the generator (you may have to charge the batteries to do this) and take voltage readings directly from the battery terminals. You should see at least 13.2 volts.

If you do not see a jump in voltage after a few seconds (10-20 seconds), then you have a problem in one of the following components: generator, wiring or one of the components between the generator and the batteries. The typical components you might find are an in-line fuse, power transfer switch, relay, diode or solenoid, and charger/inverter or converter. Your particular unit may have one or more of these components.

Good luck in diagnosing the problem. Please let us know the outcome.

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