My new battery won't hold a charge is it the alternator?

Maintenance/Repairs
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1

I just recently bought a new battery for my 79’ Firebird and no matter what I do it won’t hold a charge. I have to keep the battery on a charger all day before I drive it but even then I don’t want to keep it out long. I have a feeling it’s my alternator but I am not positive.

2

could be a defective battery, but also (more likely) could be the alternator not charging the battery. Charging it with an external charger then driving with a bad alternator (or equivalent) will only get you a brief driving time.

Could also be a cabling or similar issue. Take it to where you bought the battery and ask for a test of the charging system.

You could also buy a plug in voltmeter and monitor the battery voltage. That could help narrow it down. about $10. Here is one:
https://www.amazon.com/IZTOSS-Universal-Cigarette-Thermometer-Temperature/dp/B014MCRPT0/ref=sr_1_6?ie=UTF8&qid=1503151820&sr=8-6&keywords=car+voltmeter+cigarette

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+1
And, the OP should consider the possibility that the old battery died because of a failing alternator.

4

i had a 79 camaro. from arizona. which is nice in mn. took alternator apart and brushes were gone. worn down to spring which wore a small groove into armature. easy fix. of course i did not drive long after alt died. as battery was dead soon after.

5

Do you know how to use a shop volt meter? If so, the battery posts should measure about 12.6 volts first thing in the morning, before using the car. After you start it up, they should measure 13.5-16 volts. If they do, that means the alternator is probably working ok. If they measure below 13 volts with the engine running, the alternator or the wiring between it and the battery is the problem. Many auto parts stores, even tire stores, offer a battery and charging system test as a free service.

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When I drive it, I usually am not out long, just quick trips to the gym or store. I at first I thought it would be wiring because the guy who had it before me was in the middle of restoring it and left some wires loose. Im probably going to bring my old alternator to the auto parts store and have them check it just incase.

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when i first bought the battery that was my first thought but then I brought it back and they said everything was fine with it, it had just been drained.