Battery keeps losing charge

[Brenden Sprague]

Battery always dying cant find the leak. I just bought a battery from OReilly about a month ago and about three days after installation with minimal driving my car wouldn't start. I jumped the car and had it run for a good fifteen min and then turned it off to see if it holds a charge. The car struggled to start but I didn't think anything of it. Lucky me I was on my way to oreily but my e30 died again at the store. The guy said it was most likely a bad battery and he gave me a new one. It was fine for a few more days but now it won't start again and even struggles after a jump. I've tested the alternator and its fine. I just don't know what could possibly be stealing the power. Another observation is that there is a lot of battery acid around the battery. Could it be possible they are giving me the wrong one? TLDR my battery keeps dying and i dont know why. Any suggestions where to look?

[ELVA164]

You have a parasitic drain. Search for that term in this subforum and you'll find multiple threads detailing how to diagnose and fix your problem.

[323i E30]

You have a parasitic drain. Search for that term in this subforum and you'll find multiple threads detailing how to diagnose and fix your problem.

+1

open a window or make sure you have the car keys out of the car, then connect a milliamp meter between the negative pole of the battery and the battery earth lead, and remove fuses until you find where the drain is. Normal quiescent drain on an E30 is around 30mA.

[richardodn]

Considering how fast it's going out, it would have to be a pretty big drain.

Basic testing
1. Fully charge your battery using an external charger. Disconnect the charger.
2. Measure voltage across the terminals. It should show at least 12.5V.
3. Start the car and measure across the battery terminals again. It should read well over 13V. If the car had a hard time starting on a full charge, that points to a bad starter or bad connections. If you don't see over 13V at idle, this points at a bad alternator.
4. Rev the engine to around 2500 RPM. Voltage should be above 14V. If not, alternator is suspect.

If things are pointing to a alternator issue, make sure the battery light in the cluster comes on when you turn the key to run before you start it. Once started then the light should go out. If the light didn't come on, you have a problem. You likely have the older cluster that requires a working lamp in order for the alternator to charge.

If all this stuff checks out, go make sure ALL the high current connections are clean, snug and in good condition.
1. Battery posts
2. Negative cable connection to chassis
3. If you have a trunk mounted battery, then the junction block on the firewall. Depending on year and model, there may actually be two circuits from the battery. The main lead that eventually goes to the starter and a smaller lead for the injection electronics.
4. Main terminal on the starter. This is the one where the main battery lead and alternator lead connect.
5. Alternator connections. Especially the thicker one.
6. Main engine ground strap. This is the one down by the motor mounts. Not the one that attaches at the valve cover.

[heifetz17]

My vote goes to the alternator. If you jumped it and ran the engine for 15 minutes and it barely restarted the alternator is not properly keeping the battery charged and it will drain pretty quickly. See the above post for proper testing.

[NC540]

You have a parasitic drain. Search for that term in this subforum and you'll find multiple threads detailing how to diagnose and fix your problem.

this