Does anyone have any idea what would cause a suddden battery drain? I have a 94 f250. The battery charges up fine and holds a charge until I put it back in the truck, then overnight it is dead. Any suggestions are much appreciated!

 

Take a multimeter and measure the amp draw with the Key OFF. To do this put the meter to DC Amps and put your meter leeds in the correct sockets. Hook up your positive cable to the battery and put your meter in series with the negative cable and the negative post on the battery. While you have the meter hooked up start pulling fuses untill the meter goes to zero. Remember to have the key Off.
This will allow you to narrow your seach to 1 circuit. Then you can go from there.

 

Thanks BigBlue, Ill give it a try!

 

What's the voltage on the battery with the truck off and running? Also, pop the vent caps off the battery and measure the voltage between each two adjacent cells (1-2, 2-3, ...5-6) and tell us the 6 numbers you get for those.

This is an easier/quicker check and should be done before the other one mentioned to make sure the battery is good first before you start looking for parasitic drains in the truck's wiring.

Jason

 

Actually the quickest test would be to see if the truck has an amp draw while the key is off. If you have an amp draw look at the truck.....if you don't have an amp draw look at the battery.

 

Not to be argumentative, but an amp draw test requires the removal of a battery cable, which can be easy (or a major PITA), but checking the voltage of a battery and its cells doesn't require anything other than the voltmeter. Maybe a pocket knife to pop the vent caps off. Plus, the battery itself is a much more likely candidate for a problem. In hundreds of thousands of miles of driving, I've never had a parasitic drain, but I have replaced quite a few batteries--every 3-7 years, depending on the vehicle and battery.

Jason

 

ok my truck does have a draw, the battery is brand new and has done perfect in my ranger ( its a 65-n, which is called for by the 250) but i put it in my 250 yesterday to move it around, it started perfect, left the battery in it overnight and today its dead as can be, my question is do i have to remove a battery cable to do the test as described by bigblueox?? if so would it be the negative i assume i would disconnect

 

You can do it on the positive or the negative but the negative is safer. And yes you have to take the cable off because the meter has to be in series in order to read amperage. They do make a inductive style clamp meter for measuring DC amps but they're pretty expensive for how much you would use it.

 

What voltages did you get on each of the cells? I had a fairly new battery that showed every sign of a draw--until I checked the voltages on individual cells and found a short internal to the battery.

Jason