Troubleshooting 12 Volt Auto Battery Chargersby Alibaster Smith
Troubleshooting a 12-volt battery charger is relatively easy. But you'll need a voltmeter to troubleshoot most chargers. Since the charger is responsible for charging your vehicle's battery, you want to make sure that it is working, that there is no resistance in the lead wires, and that the voltage coming out of the charger is what it should be.
Set the dial on the voltmeter to "Ohms" and test the voltmeter. Touch the leads of the voltmeter together. The reading should be "0.00," but a variance of .05 is acceptable. "0.00" represents the resistance in the wires. No resistance means that an electrical current can pass through the lead wires the way it should without any resistance and that there is good connectivity (there is no break in the line).
Touch the lead wires on the voltmeter to the lead wires on the 12-volt auto battery charger. It does not matter which lead on the voltmeter touches which lead on the battery charger. All that matters is that one lead touches the power lead on the charger, and one lead touches the negative lead on the charger.
Check the resistance. The voltmeter will display a reading when the leads are touching the leads on the battery charger. A variance of .05 is acceptable, but the resistance should be "0.00".
Set the dial to the highest volt setting on the voltmeter.
Turn the battery charger on. Set the charger to charge at a specific voltage.
Touch the power lead on the voltmeter to the power lead on the battery charger. Touch the ground lead (the black lead) on the voltmeter to the negative (or ground) lead on the charger. The voltage output on the voltmeter should be the same as the voltage setting on the charger. If it is not, the charger is malfunctioning and must be replaced.