The Digital Voltmeter is still the most valuable tool in the Mobility Technician’s arsenal for sealed batteries. The starting point for checking batteries is always the charge voltage. In 24-volt systems 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 or if either battery is bad. This is accomplished by checking the voltage of each battery separately.

As illustrated in photo 1, voltage for a pair of batteries can read in excess of 24-volts which can incorrectly be assumed to be a good set. However, as shown in photo 2 one battery has a voltage of 12.89 volts while the battery in photo 3 is reading 11.97 volts. Combined, the voltage of this set of batteries looks good, but clearly the battery in photo 3 is bad.

Two batteries in a 24-volt system charge and discharge together almost as one 24-volt battery. A wide voltage separation between two batteries 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 wiring or other components of the wheelchair?

You can determine the next step in the troubleshooting process once you know the voltage of each battery.