Battery goes dead, no obvious reason.

[Kern Dog]

Hey there.
My 75 Power Wagon sits most of the time. I use it to haul junk and landscaping waste for trips to the dump.
The truck has a 440 and a stock ignition and charging system. When running, it charges fine but after sitting a couple weeks, the battery is too discharged to start the engine.
At first I suspected a weak battery but I switched to another one and it also discharges. I’ve resorted to pulling the positive cable from the battery after parking it.
I mentioned this on the truck forum and one member blamed the alternator. I admit to not knowing as much about electrical systems as I do about other things. To me, if an alternator is charging, it is okay.
Is that wrong?
Can an alternator actually discharge a battery with the engine off ?

 

[493 Mike]

Hey there.
My 75 Power Wagon sits most of the time. I use it to haul junk and landscaping waste for trips to the dump.
The truck has a 440 and a stock ignition and charging system. When running, it charges fine but after sitting a couple weeks, the battery is too discharged to start the engine.
At first I suspected a weak battery but I switched to another one and it also discharges. I’ve resorted to pulling the positive cable from the battery after parking it.
I mentioned this on the truck forum and one member blamed the alternator. I admit to not knowing as much about electrical systems as I go about other things. To me, if an alternator is charging, it is okay.
Is that wrong?
Can an alternator actually discharge a battery with the engine off ?

If you disconnect the ground cable at the battery and slowly touch the terminal to the battery-does a small spark occur? If so start pulling fuses, one at a time, and test for spark each time. If/when the spark stops occurring you have found the problem circuit. Now you can narrow down the culprit. There is also the possibility you have another poor battery.
Mike

 

[turbine68rt]

In addition to what Mike suggested, even if you disconnect the pos terminal, any battery will self-discharge from non-use. Some faster than others, such as a lead-acid. What battery are you using?

 

[Don Frelier]

Does the horn work?
The steering wheel horn pad on that era had foam beneath the contact area for the horn button.
When the foam breaks down the relay is active all the time.
It's a possibility.

 

[ruffcut]

Get a cheap battery tender. Problem solved. I have them on all my vehicles and they use very little electric. Just saying.

 

[68-500]

I’ve heard of alt discharging the battery. Ive never experienced it. I believe its got to do with a bad diode. 12 test lightin series with a battery post and start pull fuses.

 

[davek]

Does your truck have a clock Greg? I disconnect the battery on the Bee because of the clock.

 

[6PKRTSE]

If you disconnect the ground cable at the battery and slowly touch the terminal to the battery-does a small spark occur? If so start pulling fuses, one at a time, and test for spark each time. If/when the spark stops occurring you have found the problem circuit. Now you can narrow down the culprit. There is also the possibility you have another poor battery.
Mike

I do the same but with a test light. That way from in the car I can see the light go out when I pull a fuse from inside the car.

 

[pnora]

Is there an aftermarket radio? Most all the aftermarket will have a memory draw. Those old trucks did not have any draw unless there was something on. Most common was the dome light and if that is going off by the jamb switches properly you should be OK. I can not remember if they had any key lights?

 

[6PKRTSE]

Is there an aftermarket radio? Most all the aftermarket will have a memory draw. Those old trucks did not have any draw unless there was something on. Most common was the dome light and if that is going off by the jamb switches properly you should be OK. I can not remember if they had any key lights?

Glove box light has happened to me before also. Switch needed adjustment.

 

[Don Frelier]

Maybe it's those rats again?
Charging up their cell phones when you're not around.

 

[68-500]

Maybe it's those rats again?
Charging up their cell phones when you're not around.
View attachment 1624449View attachment 1624450

BINGO we have a winner!

 

[MWbirdLOVER70]

Does your truck have a clock Greg? I disconnect the battery on the Bee because of the clock.

I was gonna replie that too. My quartz conversion drains her over time. I either disconnect or as a buddy did he wired in a toggle switch to his clock and problem gone but had to set the clock each time thou

 

[MWbirdLOVER70]

Maybe it's those rats again?
Charging up their cell phones when you're not around.
View attachment 1624449View attachment 1624450

Little humor never hurts lol

 

[toolmanmike]

THat reminds me. I need to get over to the storage garage and put the chargers on.

 

[72RoadrunnerGTX]

Really need to do a proper diagnosis, forget about the test light, break out the digital VOM, configure it for amps. Connect it between the battery post and the disconnected cable. How much current draw while at rest? Careful not to try to start it or activate any big loads with the VOM connected as described, most are internally fused for about 10 amps max. A potentially shorted alternator diode would drain the battery at a faster rate than two weeks.

 

[eldubb440]

A potentially shorted alternator diode would drain the battery at a faster rate than two weeks.

maybe it does, and he doesn't know it

 

[451Mopar]

Can an alternator actually discharge a battery with the engine off ?

yes

 

[WileERobby]

Good replies here, but I would not just slow-charge the battery. You need to search for the draw, whether it's a faulty alternator, or another component thats eating up the battery charge.

 

[Car #4]

Get a cheap battery tender. Problem solved. I have them on all my vehicles and they use very little electric. Just saying.

But that doesn’t solve the problem. A good battery won’t go dead in two weeks unless there’s a draw on it.