Bad battery or alternator?

[Oldguy]

So I went out to start my truck and the battery was completely dead. As near as I can tell there was nothing left turned on that would drain it. It sat for more than 24 hours and there was not volltage at all when I put a volt meter on it. Charged it for 12+ hours and the voltage was up to 5.84 volts. The charger was a small one but has charged dead batteries before with no problem. Took the battery to Autozone where I bought it two years ago and found the warranty was still good for two more years. They charged it overnight on their charger and called this AM to tell me it was a good battery and had tested good. BTW the alternator was charging at 14.3 volts prior to this event.

We'll see what happens when I re-install it. Has anyone had shorts that drain a battery with all circuits off and the key out? If so can you point to something to check for?

 

[Bob L]

Easiest way to check for a drain is to disconnect one battery cable and put a meter between the cable and bat. It will tell you how much draw you have. Make sure all lights are off and doors closed. If you don't have a meter use a test light if it shines bright you have a draw a dim light is radio memory and normal. If in doubt remove radio fuse to eliminate that draw.

 

[90halfton]

Easiest way to check for a drain is to disconnect one battery cable and put a meter between the cable and bat. It will tell you how much draw you have. Make sure all lights are off and doors closed. If you don't have a meter use a test light if it shines bright you have a draw a dim light is radio memory and normal. If in doubt remove radio fuse to eliminate that draw.

What that guy said

 

[Oldguy]

Easiest way to check for a drain is to disconnect one battery cable and put a meter between the cable and bat. It will tell you how much draw you have. Make sure all lights are off and doors closed. If you don't have a meter use a test light if it shines bright you have a draw a dim light is radio memory and normal. If in doubt remove radio fuse to eliminate that draw.

Pulled both RADIO (17) and RADIO BATT (19) fuses and still had a bright light. I suppose the thing to do now is start pulling the rest of the fuses to determine which circuit is drawing power? I am doing this in stages because it is 15 degrees outside and my old fingers freeze up when I stay out too long. Did I say how much I envy those guys wtih heated garages?

 

[cookseyb]

If the voltage regulator is stuck (sealed in) it will draw your battery down in a day or so.

 

[Oldguy]

I did pull and check every fuse for a ground with test light connected to battery positive post. No circuit was found grounding battery. Had Autozone check the alternator as well and because it was noisy they replaced it under warranty. (Gotta love their warranties!) Anyway after putting evrything back together the original dead battery problem has not resurfaced.

I do not understand the post about a stuck voltage regulator. My understanding is that it is a solid state device inside the alternator itself.

 

[ram1220]

I had a similar issue with my 90 Sierra a few years ago. Drained even a new battery. Turned out to be the glove box light. I just pulled the bulb out and problem solved. I didn't need that light anyway. Just something else to check.

 

[Oldguy]

That is something I did not think of. You would think that testing all of the circuits with a hot test probe would reveal anything that provided a ground. Anyway I'm good now and will just have to wait and see what happens from here.

 

[df2x4]

Another thing to check would be your under-hood light. The one in my red truck was very touchy, if I parked facing uphill it would stay on. Had that drain my battery a few times before I figured it out. It's got a mercury switch or something similar that senses angle and turns on/off accordingly, so you can just bend the housing a little as needed.

 

[jmig]

I'm having a similar problem on my 89 dually, using the test light method pulled all the fuses one by one and the test light is still bright. I disconnected the harness where it passes through the cab under the master cylinder to help me eliminate it being anything related to inside the cab and the test light is still lit. I thought this would narrow my search down to the engine bay and started unplugging things and nothing turned the test light off. I removed wires off of the alternator and starter as well.

I then proceeded to the junction block on the fire wall and when I removed the wire that has the fuseable link which is running from the positive cable the light went out. I am going borrow a volt meter and check the amount of draw is pulling in hopes of narrowing down my issue.