My truck is eating batteries!
 

So I put an optima red in about a year and a half ago. My 87 Toy with the 22R was going through major restore work so it just sat and sat and sat. When I tried starting the truck: dead. Battery would not charge. Took it back to Ghetto Zone and they said it exploded on the charging station. Gave me a new one, thought it was a bad battery.

So I put it in the truck and just a few weeks later (still did not drive it much) this one was dead too. Tried charging and nothing. I took it back to the Zone today and they said it was bad. Gave me another.

Now my 87 is a pretty plain jane model so there's not a whole lot going on. I have no accessories in the truck besides an aftermarket CD player and it has been unhooked the entire time.

Any thoughts? I'm thinking a short somewhere? But I'm not sure how or where to start? Any electrical gurus out there with some hints? I would like to figure it out before putting the new one in.

Thanks-Dave

the simple test for checking if there's a constant and unwanted draw on the battery is to pull the negative terminal and put a test light in between. if it lights up, there's a draw somewhere.

start pulling fuses until the light goes out, and you've found the circuit to investigate.

Don't forget to disable your dome light / door open lights, to eliminate that live circuit draw first, while you are working on the diagnosis.

Yep, likely some small steady current drain. Only takes like 50 mA (0.05 amps) to kill a battery over 2-3 weeks. The Red Tops do not like being fully drained, pull them down too low even one time and that is it.

Hook up an ammeter in series with the battery cable with everything off and see what reading you get. And you might have something like a relay sticking on. A guy in my 4WD club has a Jeep with that issue. If he just shuts off the engine, the battery will be dead in a few weeks. But if he disconnects the battery and reconnects is, that stuck relay resets and turns off so all is fine. For that test, you would need a clamp on DC ammeter to be able to measure the current w/o disconnecting the cables. An alternate is you could connect a small gauge wire between the battery post and the battery cable clamp prior to disconnecting it, to maintain the current. Then disconnect the cable, hook the meter up between the end and the battery then disconnect the small lead and check the current. Usually you'll see a small current like 10-20 mA to keep things like radio and ECU memory circuits powered.

Excellent. Thank you very much guys! I'm on vacation this week so this is at the top of the list. I'll post what I find.

you can be more specific with a Digital Multi Meter (Volt meter)

As in how to test for a current drain with a DMM? Set the meter to the highest amps (or milli-amps - mA) range and if needed, move the probes to the current plugs. Then hook one probe to the battery post and the other probe to the battery cable (which is obviously disconnected from the battery). And then any current flowing out of the battery is going through the meter and reads out on the display. Which battery post and cable? Makes no difference, pick your favorite color. Current out of the battery must equal current back into the battery in a closed circuit. If your meter only has a low mA range, you might want to first use a plain 12 volt bulb (test light) to see if there is some large current drain, as that might blow the fuse in the meter if you try to check it. If your test light comes on really bright, something is pulling a lot of current, so find out what first. Pull fuses and disconnect circuits until the test light dims (or meter reading drops). Then figure out what on that circuit is pulling too much current.

I ran into a aftermarket radio that I had wired to constant power since it was both a regular AM/FM and a CB radio, so I wanted to be able to use it with the engine off. But it turned out that radio did not fully shut off like that, it still pulled ~50mA when off. If I rewired it to switched power, the current draw fell to nearly a few mA as I recall. So sometimes it takes some digging to find the cause of the current drain.

A common cause of a very high current drain is a shorted diode in the alternator. Those will pull a few amps as I understand. Also look at things like light bulbs inside glove box or a deck light that are not turned off when they should be.

Also when doing this test, remember that some vehicles take a little while to "sleep" some cars will show 50ma when first putting the DMM on as the computers are still working, I have seen it take about 15 min on a newer Tahoe for everything to completely shut down.

sorry, i didnt mean to set it to volts, i just heard people use other acronyms other than dmm and i didnt want to screw with anyone, obviously I did just that. my bad!