Bad alt or bad battery?

[CHUCKmfnNORRIS 10+ year member]

I just recently upgraded from a 700watt system to a 1200watt system and my battery needs a jump start every 3rd or 4th start. i don't know if the alt is not strong enough or if the battery is too weak.

once i jump start it i have to keep the rpm's up around 2500rpms for 20-30 minutes or it will die.

if it makes a difference i own a '99 wrangler with a basic interstate battery and a factory alt

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[trumpet 5,000+ posts]

If your alternator isn't or wasn't dead it at least wants you dead. Stop forcing your alternator to recharge your dead battery. If you can get your vehicle to a shop, find a place that can test your alternator and battery. Be prepared for the worst. A battery store such as Interstate Battery will be able to help.

 

[azphat12 10+ year member]

I would take it to autozone or checker and have them test it. Going of prior experience when my battery died, after I jumped the car it ran fine. The alternator took over running the car after it was started. I would think that your battery is dead if your having trouble starting it...maybe a bad cell or something. Just a guess though But revving to 2500 to keep it going has me stumped. I would normally think that an alternator would be going bad and forcing you to keep the idle high so it can work properly. Either way...get it tested. The meters will tell you what you need to know.

 

[05fronty 5,000+ posts]

do what they said above^ take it to one of the local auto parts stores and they can tell ya. sounds like a bad bat though

 

[CHUCKmfnNORRIS 10+ year member]

yeah im gonna bring it to my mechanic in the morning, just wanted to ask around to see what people had to say. i think its the alternator due to the fact that i have to rev the rpm's up to keep it from stalling out, i have jump started a good deal of cars and none of them required the rpm's to be reved up to charge up the bat enough to run at idle

 

[audioatg 10+ year member]

Have you check the basics. Vehicle running test the voltage at the battery and at the alternator post. See what the voltage is. Check with loads on and loads off. Different RPM,s. Also how are your grounds. Do the Big three as well yet.

As stated does sounds like a bad battery. But I would also check all you can before going to a shop and getting well you know.

 

[CHUCKmfnNORRIS 10+ year member]

the big three has been done, what do they do to check the alt? if they just use a dmm and check at idle and at different rpm's than i can do that on my own.

 

[CHUCKmfnNORRIS 10+ year member]

Bueller

 

[audioatg 10+ year member]

the big three has been done, what do they do to check the alt? if they just use a dmm and check at idle and at different rpm's than i can do that on my own.

Well they will check the voltage at your battery post and What I do is check it at the alternator post as well. If you have an amp clamp you can check your alt's amp output as well. Witch is what they will do as well.

If your alternator is only putting out low voltage at idle and higher RPM's with loads on and off, Would make me think you have a bad alt. What I mean about loads is you high beams on system playing blower on high speed. Things that draw a lot of amps

 

[CHUCKmfnNORRIS 10+ year member]

turns out that it is the battery, he is going to be able to get an interstate mega tron 34 for under $100. if i had the money i would have gone with an optima yellow top.

 

[SmartAsss 10+ year member]

if i had the money i would have gone with an optima yellow top.

Don't feel bad, deep cycle batteries are overrated. (the wrong application as a starting battery) They provide longer and lower discharge in exchange for the instantaneous higher discharge needed to start a vehicle or to feed a demanding musical peak.

 

[CHUCKmfnNORRIS 10+ year member]

the batter im getting is a deep cycle battery, it had just about the same specs as the yellow top.

 

[CHUCKmfnNORRIS 10+ year member]

just installed my new battery i just got. paid $105 after tax and return of dead battery. its an interstate mega tron plus, 880 CCA can't remember the rest of the specs but its got better stats than the optima yellow top d34.

 

[SmartAsss 10+ year member]

interstate makes very good s***, very good choice.. I would buy a interstate battery over any of the "audio" branded batts.

 

[abb1771 10+ year member]

Simple Test:

If you want to see if your alternator is producing current, turn on your headlights when you're parked and the engine idling with the headlights shining on a wall (at night). Notice how bright they are. Then turn the engine off. The lights should get dimmer when you turn the engine off. If the lights get brighter when you kill the engine, the alternator was not charging sufficiently. When doing this test, the lights should be the only load (turn the stereo, a/c and other accessories off). With a heavy load, an otherwise good alternator may not be able to produce sufficient amounts of current at idle.