How can I tell if I have a battery problem or a charging problem?

A voltmeter is still the most valuable tool when troubleshooting sealed batteries. (see “How can you tell if a battery is fully charged?” above) When checking batteries always start by checking the voltage. In multi-12 volt systems such as a 24-volt system, we know the chances for two bad batteries are less than 1 in 10,000. So what we need to determine is which battery is bad, if either battery is bad or if something else is wrong. This is accomplished by checking the voltage of each battery separately. We can not just check the total voltage. We might incorrectly assume the bank is good when by checking them individually we find that one has a voltage of 12.70 and the other a voltage of 12.1. Combined they looked good, but separately they were not! Multiple 12 volt battery banks charge and discharge together almost as one when hook in series. A wide voltage separation between two 12 volt batteries in a 24 volt system indicates that you may need to replace both batteries. If both batteries read similar voltage, they should be fully charged before doing any further testing. If both batteries are below 12.0 volts, the question becomes, why?” Is the battery charger working correctly? Could there be a problem with the applications wiring or other components. You can determine this once you know the voltage of each battery.