a1so

Hello everyone. This is my first time posting and I'm really hoping you guys can help me. I very recently purchased a 93 SC400. I drove it home two hours, it ran great and had no issues. The next day it started fine, but as I did some errands weird stuff started happening. My dash lights gradually got dimmer, flickered with the turn signal, and when braking they got very dim and battery light came on. When stopped at a light, dash was very dim, batt light on as well as some other random ones (ABS, Trac, Trac Off, CE light) and the engine idled really low, almost dying but it never stalled. When I got home, it wouldn't even crank again. I put the battery on a charger, it was super low but took a charge, albeit slowly. When I put the battery back in it fired up great. The next morning, it started good, but again over the course of about 2 hours of errands the same issues as above started to appear, culminating in me writing this post in my driveway with a dead battery. When idling the battery shows 13.2-13.8V, and at 3000RPM it's 14V, which indicates to me it's charging. I have no idea what could be causing this, and any help would be massively appreciated.

mmarshall

Welcome to CL as a new poster.

Obviously, with a 30-year-old car, you are going to be taking some chances. It sounds to me like you may (?) have what is called a slow "parasitic" drain on the battery. This can come from a number of sources, but common ones are glove-box, underhood, and trunk lights that are stuck on...they drain the battery at a very slow pace, so that it may start your car for a while after a recharge, but not after sitting all night or for a few days.

This can be hard to detect because, of course, it is not easy to see inside compartments to check the light bulb after their lids have been closed. The best way to do it is to close the lids very slowly and look through the crack just before it clicks shut.

isfvss

Sounds like the battery is cactus.

a1so

Thanks for the reply and for the welcome. I had considered parasitic load, but the fact that it seems to be losing juice so quickly, and kept charge well overnight then began losing power while driving, led to me thinking it probably wasn't that. Under further inspection, the belt is loose, shows signs of slipping, and the tensioner moves a lot, both when the belt is pulled on and when the motor is revved. My working theory is that the tensioner is shot, and when the alternator is under load the belt is slipping and it can't charge the battery very well. Going to replace belt and tensioner to check this theory, really hoping I'm right.

a1so

I am considering that too. The battery took charge and didn't throw any warnings on the smart charger, but I still think I'm going to get it load tested to be safe.