battery/alternator issue

96 XJ w/ 4.0

i have an older battery that gets drained by the cold, which makes the engine struggle to start if i haven't driven it in a few hours. charging the battery fixes this problem, which is how i know my battery is low. after struggling to get the jeep started, i left my driveway, and before i got out of the alley the jeep died. jumpstart didn't work, engine would turn but not start. so i replaced the alternator with a remanufactured one from autozone last weekend. that fixed the problem, jeep was running fine until today. well the same thing happened again today after the jeep took a few extra seconds to start up. it seems like it is the alternator again. checked the connections to the alternator, they are all tightly fastened...

my question is, can the lack of power in the battery ruin the alternator by making it work too hard or something?

the alternator has a warranty so i can get it replaced, but i also plan on replacing battery terminals and the battery with an optima. any help is appreciated. thanks in advance

Yes, it can.

If you replace your alternator, charge the battery before you fire it up. If you replace you battery, monitor your alternator closely for about a week.

What happens (as I recall,) is that when the battery gets low, the regulator will shove the alternator over to full output to try to charge the battery. This used to commonly blow out the regulator, but solid-state regulators are a little hardier than the old ones used to be.

So now, you end up blowing the diodes from overheating them.

If you take it in for a "bench test" at your local parts house, they just check voltage output - they do not check the output current of the thing. You'd have to go to a specialty shop for that. I bring this up because, just because it "passes" on the bench, that means it's generating somewhere between 12.6-14.5 volts at about .01A. They don't have a way to actually test the thing at full load/output - nor, honestly, does higher-higher want them to.

I've had to fix the bench in most common use - that's how I know. Wasted three and a half years working at a "chain" parts house (Checker/Schucks/Kragen's/Northern Automotive,) so I've got a pretty good idea...

Yes. A bad cell battery or dying battery can and will toast your altenator. U can have the alt load tested and also battery. Probably need to replace all like you said.

5-90 said:

If you take it in for a "bench test" at your local parts house, they just check voltage output - they do not check the output current of the thing. You'd have to go to a specialty shop for that. I bring this up because, just because it "passes" on the bench, that means it's generating somewhere between 12.6-14.5 volts at about .01A. They don't have a way to actually test the thing at full load/output - nor, honestly, does higher-higher want them to.

Click to expand...

Yup. I just had mine rebuilt at a local specialty shop. When he bench tested it, it was putting out just over 13 volts but only 3 amps. Your chain store would not have found that.

Incidentally, I asked about upgrading it, thinking I had the 61ish amp unit when I really had the 105 amp model, so I almost ripped myself off by getting a reman at a parts store.

Basically, your battery powers all of you car's electrical components at a steady 12-14 volts(more or less). If your battery is bad and doesn't put out the required volts, then your alternator works hard trying to recharge your battery, and put power to the rest of the electrical components. This is not only hard on the alternator, but can strain and possibly damage other parts of the electrical system, including your engine ecm computer, because the alternator's voltage output can vary significantly instead of the batterys steady 12-14 volts.

If you go with the Optima, I would suggest the red top instead of the yellow top. I have had two yellow tops go bad within two years of service.
The yellow top only has a 1 year warranty, whereas the red top has a three year warranty. I am sure that the yellow top is a fine battery, but in my experience, they don't seem to come back very well from a complete discharge. Of course the Optima(or any dry cell battery) is a good choice for off road usage, because there is no chance of battery acid leaks on extreme angles. One other thing on dry cell batteries, I read somewhere that you should only recharge a dry cell at a low amp charge, and that a high amp charge risks damaging the battery. I don't know if that is true or not. Does anyone know the answer to that question?

Good luck, and have fun on the trails.

a long slow charge is the best charge for all batteries I think, it helps them maintain there ability. I dont have any backup, just experience of charging some. :cheers:

I don't think I've ever heard of a just plain dead battery toasting an alternator, and in all my years of running dead and dying batteries I've never once burned out an alternator. One of the main advantages of an alternator is that unlike DC generators, they do not require current regulation.

However, if the battery is shorted or has a shorted cell, all bets are off, although I've also never lost an alternator to bad cells either, though I've had a few batteries that were definitely shorted.

I'm more inclined to believe that a bad alternator will kill the battery than the other way around.

A battery so dead that it will not accept a charge at all can lead to overvoltage and transient spikes in the electrical system, which in some cases will cause damage, and in others will just cause bad running, stalling, etc.

The voltage regulator for an alternator is not in the charging circuit itself, and only switches the field on and off to control voltage, so even if current draw is great enough to cook an alternator, it should not affect the regulator.