How to Test a Battery Charger. If you're unsure whether your battery charger is working properly, there's an easy way to find out. Running a test on your battery charger is an easy process.
Plug in your charger to an electrical outlet. Remove any batteries you may have charging in the unit.
Turn on your voltmeter unit. Be sure there's power getting to the meter. Plug in the test probes into the voltmeter according to the meter's instructions. Set the selector switch to the highest level for DC Volt or whatever is recommended in the meter's instructions.
Take a battery or battery pack that's compatible to your battery charger. Make sure the battery has no corrosion and is not leaking fluid. Touch the positive end of the battery with the red probe. Take the black test probe and place it on the negative side of the battery.
Check the readout on the voltmeter and see where the pointer is indicating to. If it's on the left side, or negative side, switch the test probes. If it's on the right side, it will show that the battery is receiving some charge. Where it points to on the meter will determine how much charge it received.
Check the battery charger to see how much power it's giving off, if you continue to receive a negative reading from the batteries. A negative reading will indicate a bad battery charger, and you should replace it. If the charger has sufficient amount of power flowing through it, it's more than likely the batteries are bad and just won't hold a charge.