Check a 12-volt battery by disconnecting it from the device it powers, take an initial reading, charge it and take a second reading after the battery sits. Reconnect the battery, attempt to start the device and take a third reading.
- Take the initial reading
A fully charged 12-volt battery should read 12.66 volts. Any reading below 11.89 volts indicates a fully discharged battery.
- Charge the battery
Connect the battery to a charger, and allow it to charge completely. Allow it to sit for eight hours before testing again.
- Reconnect the battery, and test with a load
Reconnect the battery. Disconnect the ignition wire from the coil. Turn on the key for no more than 15 seconds, and read the meter. If it drops below 9.6 volts, it is bad. Batteries that remain at 9.6 volts or above are good.