battery or alternator?

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

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.

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

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.

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.

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