How to test to see if you have a bad battery or bad alternator

Asked by Jun 29, 2015 at 11:11 PM about the 1997 Ford Crown Victoria 4 Dr LX Sedan

Question type: General

I started the car disconnected the battery
the car shut off within 20 seconds I believe
its the alternator I've taken the battery down
to the local auto parts store and they tested
it and they said It was good and within
range. But the battery was to low to run test
On the alternator so I have the battery On a
charger

2 Answers

102,245

First of all never ever disconnect a battery cable with the engine running, you can cause a voltage surge that can fry electronics. I had a customer that did that to his crown Vic and it wound up costing him 1500 bucks to get it running again. The proper way is to have a shop check the system on these high output charging systems, most of them are now computer controlled, so even thought the alternator checks good out of the vehicle it still may not work when in the car. You can check the battery the old school way by making sure it is fully charged, then just turn on the headlights with out the engine running for 20 minutes, if will crank over the engine the battery is strong enough to run your vehicle, if it don't crank it replace the battery. Or your local parts store can run a load test on it to see if it can handle full load or not. HTH

1 of 1 people found this helpful.

Thank u will try that . I'm charging the batter now

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