Dead Battery

[LouF]

Here's the story: Used car as normal, the next day the battery was flat dead; Charged it; The next day it was dead. So I disconnected the positive and the standing battery and am charging it now. It seems to taking and holding a charge normally.

I don't think it's a bad battery because... I took an ohm meter to the positive and negative cables at the battery (positive disconnected) and measured ~430 ohms; Re-hooked up the cables, and started the car. Then disconnected the battery again, and had a short-circuit reading at the (disconnected) cables.

I normally run an Aerotech scanner which plugs into the OBD port and continually reads. It shows no DTCs. I was expecting to see a P2503 ("indicating that the charging system is no longer producing the correct voltage to sufficiently charge the battery", or a P0562 "System Voltage Low".

My postulation is a bad starter motor.

Thoughts? Thanks.

Oh, 2005 GTP, second owner, have had it for many years, 120,xxx miles, only 1 battery replaced since I've owned it, assuming original alternator and starter.

 

[Scottydoggs]

load test the battery, most parts stores do this for free.

car running at idle, you should see at least 13 volts, to 14. car off you should see 12, sometimes 11.7.

 

[GTPNovak]

Harbor Freight sells a load tester that works well for like 20 bucks. it can check battery and alternator. good investment if u ask me.

 

[stealthee]

Its not the starter. It's either the battery itself, or something killing the battery.

You need to do a parasitic draw test.

This video shows a step by step https://youtu.be/KF1gijj03_0

 

[LouF]

Yes, I'm back to suspecting the battery. That would be nice. After reading some other stuff, it's said that starters do not typically fail like this nor alternators (diodes fail as open). I put an ammeter between the ground terminal and the cable, and am seeing ~ 0.03A draw. A stereo sub-woofer tube amp seems to 0.01 of that. I'm going to let the batt. set tonight, and go from there.

A heads up on digital meters and systems. I noticed initial readings of ~1.4 - 1 amps when the ammeter was first connected. I don't know if its the meter settling down (this definitely happens with ohms) or systems going through whatever algorithms, but these readings come down after about half a minute. I could hear systems energizing as the meter gets connected.

Thanks for the replies. Will follow up with findings.