battery or alternator?

[7M-GTE]

Got a question and hope you guys can help me out!

how do you know if its you battery or alternator thats needs to be replaced?

Thanks

[speedracer]

Use/Buy a multimeter and test the battery and then the alternator.

Battery should be around > ~12.6 volts
(Car not running)
Lower and it could mean it's not being charged or the battery is no good.

Altenator - You need to have the car running to test and see what the output is coming out.

[T5_X]

take a monkey wrench and put it down on both terminals, hold on tight!
j/k, DON'T DO THIS!

If you find that the charge is lower than ~12.6, it could be either, even neither. Check the terminals and see if they're loose or badly corroded, also check the alternator drivebelt and see if its slipping, could also be a short in the wiring or broken wires. Check all of these, measure voltage.

[D'z Nutz]

Why don't you take it to Partsource?? They'll run some tests for you and can tell you whether or not it's your battery. The tests won't cost you a thing to do.

[T-rus]

engine not running batt. avg 12.4-13.3 V

Enging running output should be 13.5-14.7 V

If below on eather scale you have found which one is wrong. If low on batt. recharge and see if it will hold the charge.

If low on alternator replace alternator