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Battery or alternator?

Battery keeps going dead. Jumped battery, took positive cable off, car kept running, took negative cable off, car kept running. My alternator is still good right? Just need a new battery right? Sorry old age and stress is playing with my mind. I use to know this without having to think.

Year, make, and model, please. All cars are NOT the same. We need to know what you’re driving. We should also know how old the battery is.

Disconnecting the battery cables while the engine is running (on late-model vehicles, at least) is a HUGE no-no. You can cause significant damage doing that.

If the battery keeps going dead you either have an old battery or an alternator that’s no longer charging correctly.

Why do you say, “My alternator is still good, right?”

Unless you have had the alternator and the battery tested you are guessing.

Quit guessing. Take the vehicle to a parts store, or a mechanic, or somewhere, and have the battery and the charging system tested. Then you’ll know what’s working and what’s not.

1993 ford areostar, when I bought the van used the battery looked like one they bought at a junk yard, so the battery is definitly old.

Why do you say, “My alternator is still good, right?” Because with older models if the engine keeps running the alternator was good when you disconnect the cable. If I remember correctly.

Forget older models. That was then, this in now. Disconnecting the battery cables while the engine is running is NOT a good idea, and I suggest you don’t do it again.

It’s your car. Do whatever you want. But you’ll have no one but yourself to blame if electrical/electronic things are damaged.

The only way to know if your alternator is good is to have it tested. Same goes for the battery.

Quit fooling around. Have the battery and the alternator tested before this gets any worse.

You could remove a battery cable to determine if a GENERATOR was still functioning. If you remove a battery cable with an alternator, the alternator no longer detects a battery reference voltage. This causes the alternator to go to full output which causes it to overheat which causes damage to the alternator. So if the alternator wasn’t damaged before removing the battery cable, it could be now.


OK generator. Hopefully no damage to the alternator was done. I only took each cable off for about 3 seconds each. I didn’t take both cables off at the same time. Do you think 6-7 total seconds was enough to damage it?
From now om I’ll have the battery and alternator tested. thanks

Large chain auto parts stores will usually test the battery & charging system for free. They will then install a battery for free if that turns out the be the problem (and if you buy it from them, of course). Simple, quick, painless.

A way to do a quick check for yourself is to put a volt meter on the battery w/ the car off (after it has been run long enough to give it a full charge). It should be at about 12.7. Quick alternator check is to do it w/ the engine running - should get up over 14volts. But that just gives you a rough idea.

(Mcp - mellow out - the guy’s just trying to get a handle on things - outdated knowledge but you sounded a little snippy up there).

No problem with Mcp. Checking the alternator last winter may be why my radio lights and clock don’t show anymore.

I appreciate any right help I can get no matter how aggrevated they get with me as long as what they tell me is true I’m happy. Thanks to all of you.