I changed mine out a few years back , but I think it was bad batteries.

Mo

It's unusual for all banks to go out at once, but it does happen. If you suspect a particular bank, and wonder if it is the charger or the battery:

If you ever wonder if something is up with a particular bank of your charger, move the two charging leads to another battery - actually swap them completely. If the problem stays with the battery that the leads had been connected to, it's the battery. If the problem moves to the other battery, the problem is the charger bank. If you suspect all three banks, you need to check the voltage on the batteries while charging. If it's not 13 or over, something is up with the charger most likely. The specs of your particular charger will dictate what you should see.

Check the charge on your batteries..if you are having trouble charging your batteries...most multi-bank changers require at least 5 volts stored in the battery to charge the battery, if your batteries are less than 5 volts it will not charge them. You can use a single bank trickle charger to restore the charge , if the batteries are still good.

check charge on battery, if more than 9v turn on charger and check for charge voltage, should be 13.5 or more, swap banks and test all on same battery.