Batt won't stay charged overnight
 

First off, it's not an alternator problem, I can charge the battery fine if I can get the car started. It's not a battery problem, I just put this one in and it works fine, it just won't stay charged overnight.

I figure it has to be a grounding problem. Has anyone delt with this? Any suggestions on where to start looking?

Make sure the battery terminals are really tight? But make sure you didn't get a defective battery; might want to exchange if you can.

Id say you figure wrong ............... on more than one of those statements.

It may very well be an alternator problem - ie - the voltage regulator may contain a leaky diode.

And no loose connection anywhere whill drain the battery either - not on a battery post or anywhere else.

No grounding problem will ever drain the battery - ie - for a battery to be drained you need current to flow, so a dodgy connection will actually contribute to the battery staying "charged" longer by limiting the possible current flow.

After making sure you don't have a lights staying on in the boot or cubby etc etc I would remove the positive (or negative) terminal from the battery post, insert a current meter in the line and measure the current flowing there ............... I would say about 50 to 100mA is to be expected and normal if your car has an alarm/immobilizer.

If you find more than that flowing, remove the fat terminal from th back of the alternator and measure the current drain on battery again - if its less than above you know the alternator's voltage regulator could be to blame (either completely or partially) .................. if removing that cable doesn't make a change then you are on your own and will need to speak to a sparky to tackle the individual circuits and test those

i replaced my alternator a year and a half ago.

and then around december/january, my car started having trouble holding charge in the batter after sitting for long bouts of time, worsened by the cold.

eventually, my battery light was coming on and everything was running dim unless i was driving 2.5k rpms or higher, and then sometimes it would die off then.

problem? another bad alternator.

i exchanged the battery before replacing alternator only to have same problem.

alternator fixed.

Two ideas:

1. Strange, but had it happen to me... My amp had a bad ground of some type in it and drained the battery even with the car off and no trigger signal. This took a while to track down.

2. Have you made sure the colling fans aren't running continuously? If the coolant temp sensor is bad then it can cause the fans to run continuously, draining you battery.

Mike