Battery on my '74 Chevelle (Laguna) loses charge overnight.

Recently had a complete electrical tuneup done on the car and the problem did not appear until weeks later so doubt if there is a direct connection to the problem.

Battery is about 1 year old. When I put the battery on the charger it has good starting power over period of an hour or so of testing. I cleaned and tightened the terminals but the battery still loses charge. Have checked for obvious dome light and other lights left on etc and and assured as much as possible that accessories are turned off.

Would appreciate suggestions of how to trace the problem or possible sources of the problem.

Thanks!

Could be the alternator, blown diode. You can either pull the alternator and take it to a parts place for testing or troubleshoot it yourself.

You can buy or make a test light from a standard automotive bulb and socket. Remove the positive battery cable. Remove the the main positive lead from back of alternator, it's the heavier red one. Hook the battery cable back up and place the test light between the the alternator post and the cable. If it lights up the alternatore is shorted. If not then unhook the battery cable again and trace the small red cable from the battery to a junction point, not sure where that is on a 74. Remove the cable and test between it and it's mounting point. If it lights you can start pulling fuses to see if it goes out. It's just a simple process of elimination.

ALWAYS disconnect the battery before disconnecting or reconnecting alternator or electrical in car.

Larry,
Drive the car to make sure the battery is charged up, then park it and remove the battery cables. Let it sit overnight. Then connect the cables and see if the battery is dead. If so the battery is the problem, probably a shorted plate or something else internal. If the battery is ok after this test, then you will have to start isolating circuits.

Was anything new installed on the car that could have been wired so it is drawing power when the ignition is OFF when it should be wired drawing power when the ignition is in ACC or ON?

Finally & BillK,

Thanks for your excellent suggestions. Think I'll do BillK's easier test first and go on from there if it isn't the battery.

Maliblu65,

No new equipment was added and I don't think the tuneup people screwed things up as it ran for several weeks after they worked on it. Suppose it could be some sort of problem that took awhile to surface.

The suggestions you provided are very helpful!! Thanks!

Larry

Good plan and the easiest place to start. I wasn't thinking battery because you said it's one year old but it certainly could be bad. If it's ok the next easiest is just pull the alternator and have it tested.

Wanted to thank everyone for the advice and close the loop on this thread.

I did as BillK suggested and charged the battery and then unscrewed the terminal connectors from the battery and left it set (for several days as I got busy with other priorities). When I hooked the terminals backup, there was nothing--battery was dead.

Took the battery out and returned to Schucks, our local parts chain, where I had bought the battery originally. They put it on there tester and confirmed that the battery is bad. They got on their computer and confirmed that I had bought the battery less than a year ago and gave me a new battery at no expense to me. So I got it resolved with minimum bother and no out of pocket payment. Of coarse it's somewhat disappointing that the new battery didn't even last a year and that I had to remove it and reinstall.

Thanks for your help in analyzing the problem. Guess I'm a pessimist but I about had myself convinced that I'd have to buy a new alternator.

Thanks! Team Chevelle scores again!!