Battery/alternator help please

[joker4096 10+ year member]

So i know for a fact that my car battery is almost dead, since i drained it once a few months ago by leaving the lights on, and i also had the car sitting for 3 months last year when i blew the engine. Here is the diagnosis, the car starts up fine, but when i drive the lights dim when the revs drop below 1000. The battery after sitting over night sits at 12.6 volts i believe. When coasting and i let off the gas, whenever the revs go below 1000 the lights dim, everytime. anything over 1k and hte lights do not dim at all. Sometimes if the revs drop low enough, the car will feel like it will stall out and sometimes it does. What do you all think is the problem?

please, any input will help

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[jco1385 5,000+ posts]

bad alt/bad battery/both

 

[KyleBechtold 5,000+ posts]

what kind of car? stock or aftermarket alt?

 

[bigbangtheory 5,000+ posts]

Do new battery first, if still doing it, then most likely you have a bad alternator.

 

[joker4096 10+ year member]

honda civic, stock alternator

 

[loopkiller 10+ year member]

Sounds like the alt is going bad. Have it load tested at Vatozone.

 

[joker4096 10+ year member]

ok so today i went to start the car, voltage was at 11.8 volts, then when i started it up, 13.6 and driving 13.6. when i let the revs fall, it goes to low 12 volts

 

[Bassman999 10+ year member]

Charge batt fully with a charger. alt cant do that you know. Then test voltage if still 11.8 after a full charge replace battery.

 

[loopkiller 10+ year member]

ok so today i went to start the car, voltage was at 11.8 volts, then when i started it up, 13.6 and driving 13.6. when i let the revs fall, it goes to low 12 volts

11.8V is to low. Either the battery is shot, or the alt is no good. Have both load tested at Vatozone.

 

[joker4096 10+ year member]

Ok so i did the big 3 (was actually 4 wire upgrades) today and gained a few points. with the engine running at idle it was at 14.1. so that helped a bit and later I'm going to get the load test done