How to test an battery charger (automotive)

Factual Questions
1

I have an old battery charger that I think may be dead. I also have a car battery that may be dead. I could hook up the battery for a while, but have no way of telling if the battery is shot and won’t take a charge or if the charger is dead and won’t deliver a charge. The suspicion of mortality is not related to either unit (I had trouble with the charger on a different vehicle; the car battery just died and I’m not yet sure why).

I have a handy dandy home multimeter, and can take either or both battery and charger to Autozone if there’s something they can do. Is it worth the trip?

Thanks,

Rhythm

Oh, and does anyone know why our car won’t start? :slight_smile:

2

Plug in your battery charger (with no battery), and put your multimeter across it (set to the 20V DC range). You should measure ~13V if the charger is working.

Use the same setting across your battery to see if it is flat, too. If it is, and the charger is working, hook it up overnight to see if the battery will hold the charge.

And your car won’t start if you don’t say “please” :wink:

Si

3

Check for no load voltage first, it should be in excess of 14 VDC.

Check your battery voltage.
Connect to battery and check voltage again. Charge overnight.
With charger connected in morning check voltage again.
Disconnect and check the battey’s voltage.

And always talk nicely to machinery.

4

If you’re not sure about the condition of either your car battery, and/or your battery charger, and you said you already have a voltmeter:

  1. With car off and no charger connected to it, meter the battery for voltage. Should be around 12 volts DC, give or take. Lower voltages would say your battery is probably discharged.

  2. With the battery charger connected only to your voltmeter (not to the car), plug it in and test for voltage.

Or, a cruder test but it still works:

  1. Turn on car’s interior light or parking lights or any other light. Does it work? If so, you at least have some kind of charge in your battery, even if it’s not enough to start the engine.

  2. Attach battery charger to car, and then plug it in, while observing the car’s lighting. Does the car’s light get brighter? If so, the charger is probably good.