Bad alternator/battery?

[clbailey]

So I went out to my car after it sitting for a week and it had a dead battery. I was in a rush and didnt actually diagnose it since the battery was from 08. I bought a brand new Optima red top put it in and it fired right up, car sat for a few more days till I went to crank it and it was very low on juice.

Can I test the system to see if its the alternator by pulling the negative terminal off the battery while its running to see which one it is? I highly doubt the Optima is bad from the factory. It seems there is a parasitic loss while the car is sitting more than normal but the car is electrically stock so it shouldnt be doing anything out of the norm.

It has 84k on it, is it time for the alternator to go?

 

[STAMPEDE3]

Do NOT pull the cable while running.

You will need to do a parasitic draw test.

 

[clbailey]

How do you go about doing that?

 

[clbailey]

Do alternators charge the battery a bit enough to be able to keep it running for an hour if I charged the battery with my jeep for 4 minutes? If an alternator is bad will it still charge a bit? I sprayed the crap outa the coil with electrical cleaner too.

 

[99MystiC]

Is the batt light on when the car is running? You could charge the batt with ur jeep. I had to do that at the track when my alt went out. What you can do to test is turn the car on and get a volt meter on the batt and see what volts u get. If your not getting 14 then u got a prob, but most of the time the batt light should be on if the alt is bad.

 

[clbailey]

Nope no battery light when car is running and it seems to hold a charge while running just loses juice when it sits but its a brand new battery and doesn't have any shorts.

 

[Myersprostatus]

do you have a digital mulitmeter?
get the car running and check the voltage at the battery. If the voltage is around 14v your alternator is fine.

 

[99MystiC]

I would not be surprised if the Red Top took a crap. Happened to me a while back. Same thing the batt was new and lost juice sitting for a day or two. I hate red tops esp now they suck more than ever. Go to Autozone and have them check that thing with there testers. That will tell u.

 

[clbailey]

Well the alternator is charging its reading 14.5 while running I think the red top had sat for a long time on the shelf and only had that reserve still charged and I didn't charge it enough the first tiMe. It seems to be better now.

 

[99MystiC]

Well the alternator is charging its reading 14.5 while running I think the red top had sat for a long time on the shelf and only had that reserve still charged and I didn't charge it enough the first tiMe. It seems to be better now.

Was there a build date on the batt? They usually have it on them. I would keep on eye on it.

 

[clbailey]

Not sure, I will check today.

 

[clbailey]

7/2012