I have a '94 F-250 with a 7.3 diesel.(so there's 2 batteries). I don't drive it much but if it sits for 3-4 days the batteries are drained to where I need to jump it off and let them charge. Batteries and alternator have been checked and are OK. I'm lucky I have another truck to drive, this problem has gone on for several years.

Are there ways to check for shorts and how would I track them down?

Well, you can pull the positive battery cable off the battery on the passenger side, use a VOM between the cable and the positive terminal on the battery. If the volt meter reads volts there is a drain. Then start pulling fuses one at a time and repeat the volt readings.

thanks...I'll try that.

The best way to do it is not with a DVOM since there will be some voltage/amp draw for radio memory and computers and making contact between the battery and cable will start them up. Initial start up amp draw on computers is higher than what it is after a few seconds. I recommend getting an amp clamp and using an amp clamp to determine amperage draw after the vehicle has sat for a few hours after running. It takes some computer modules a few mminutes to power down after running for awhile. I know that truck probably doesn't have alot in the way of computers but its still a good rule of thumb to follow. If you have more than an amp or 2 of draw then you have excessive draw. It should be obvious if its only taking 3 or 4 days to be dead. It would take about 5-10 amps of draw for the batteries to be dead that fast if they are good.

If you don't find more the a couple amps of draw then you need to fully charge the batteries and leave them unhooked from the truck. After a couple hours of being off the charger check the voltage of the batteries should be 12.7-12.9 fully charged. Then check the voltage again after 24 hours and see if the numbers are still the same. If you lose a few tenths of a volt over 24 hours without any connection to any electronic system then the batteries may simply be not holding a full charge. You could also go for a longer period of time as well. Batteries can test good but still not hold a charge over time.

The amp clamp is handy for checking alternators and starters too so if you do much of any work on your own stuff it would be a tool that could be handy to have.

You need to be looking for amps not volts. I dont know the spec on your ford. but anything over 50 milliamps or .05A is too much.

This sounds like it's over my head. And I don't want to be buying any tools. I think it's time to take it to a mechanic.


Thanks to those that responded.

That's why I said use a voltmeter and pull fuses.

Check your voltage regulator, a bad one will drain a battery. It's a fairly cheap fix.

+1

Isn't the voltage regulator built in the alternator? He's already said he had it checked and it checked OK.

Took it to a mechanic.

He checked the batteries and found one of them to be bad.
He said the trick is you need to disconnect the cables from both batteries before checking them. Will not show a bad battery with a load while both are hooked together.

I went to Auto-Zone where I bought the batteries in '09, disconnected the cables and had the guy check them.
Sure enough, the one on the driver's side checked bad. Got a free replacement.

I'm still keeping an eye on it, but I've gone a week a couple times letting it sit and it cranks strong.