My battery gauge in my Z has been hovering just barely above the top of the red for awhile now. I don't remember it being that low before. My question is: When this happens, does it mean that my alternator is not charging the battery, or is my battery just not hold the a charge. Im thinking that it would be my alternator... especially since it is the same one that was on the car when I got it, while I have since replaced the battery with an optima red top. (even though recently I somehow managed to completely drain the battery. It has since been put on a charger and I was told that it was fine...) Any thoughts?

 

Use a digital voltmeter to check the system. With the engine off, the battery voltage should be about 12.6 volts. With the engine running, the float voltage (alternator output) should be 13.5 to 14.5 volts.

WD

 

Optima batteries have in the past been bad(Not lasting long)..... Not sure if the problem has been corrected...

Also check for loose wiring/corrosion/wore areas on cables.....

 

I would assume the alternator. If you can jump it and it stays running, usually battery. Jump and it stalls then usually alternator. You can also measure voltage like people have said

 

the float voltage is still measured at the battery terminals correct? I dont have to track down a plug coming from the alternator and go from there do I?

 

At the battery terminals, idle, the voltage should be around 13.8~14.2.....

 

Hi i'm not sure if you have the same problem as i had but it sounds the same . My 87 camaro wouldn't charge unless it was reved past 3000rpm. altenator was checked out ok so the leccy put a low voltage light in the system (called it a exciter) and it lets the altenator think its under load at idle and starts charging straight away.No more flat batteries.Hope this helps.
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