2003 F-350
About a month ago I had a dead battery a couple of times, I ended up finding one battery that wasn't any good. I replaced both batteries.
Everything appeared fine until about a week ago.. back to dead batteries

I had the Alt tested and came back bad.. So I replaced

A day later... dead battery. Finally got it going.. took me two battery sources to get it running. Took it back in for a charging system test.

Alt came back with good voltage output
Each battery is 850 cold cranking amps... and the test showed them as 1230 cranking amp output...which I think is to high... but was told "its ok"..

After this test I ran it for the day...seemed ok. Then after it sat for about 4 hours... I opened the door to get in and no interior lights and no power at all.
Outside air temp is about 40

Everything is turned off when sitting... the only thing on is the brake controller which I'm going to disconnect today.

I'm wondering if the auto position for the headlight switch can draw power in anyway even though the lights aren't on?

Also, is there a way to test for battery drain by using a DVM?
I don't have a scan gauge.

Any thoughts?... thanks

 

The best way I have found to find a parasitic draw is to disconnect the ground from the batteries. Turn everything in the vehicle off. Put an Amp meter between the battery and the negative battery cable. You should see a draw on the meter. Then start un plugging things 1 at a time until the draw goes away. What ever makes the draw stop is your culprit. It has been my experience 85% of the time ( or more ) its the alternator. Even a new one can have a bad diode in it. The diode ( in a simple way ) makes 1 way travel for the power. So the alternator can send power to the battery, but not pull power out. I would do the above with the amp meter and start by unplugging the alternator. And yes it will drain 2 batteries in 1 day.
Good luck chasing down a ghost!!

 

Ok, so even though the Alt test good it is still possible..got it.
Just to double check... I can use the AMP setting on the DVM?

 

yes you can. Also dont make the mistake of checking the amps on the battery with the DVM. you will end up replacing the fuses in your DVM. Red lead on the battery - black lead on the battery cable will get you what you need. I was doing this procedure one time and a buddy of mine grabbed my fluke and checked my battery amps for me. My next trip was down to the store to get 2 fuses for it..

 

Well here's my results

Both positives connected to batteries
Both negatives disconnected from batteries
DVM set to 200MA scale

0.00 with everything off
0.00 as I turned on different switches..

back to the beginning I guess

 

Before performing this test I charged one battery over night on 10 amp, and then charged up the second battery for an hour

After getting all zeros on amp draw I reconnected the battery and tried to start "click, click"

Hooked my 900 amp jump start to one battery and connected the battery charger to the other and set to jump start.... same thing, "click click". All my gauges do wacky things... can the starter be shorting the system out? But would I notice that on the AMP draw down test?

Where should I go from here?


If I hook up an actual vehicle to it... after about 15 min's I now it will start... just isn't making sense to me

 

maybe a stupid question, single or dual alternator?

 

its single alternator

 

Somthing went wrong with the test or you have a terrible connection (likely ground) issue or your meter's fuse is blown. All modern vehicles will have a small drain. Here is chart with some general expected draws.



With one of the cables disconnected from the driver side battery- it doesn't matter which one, you just don't want it to contribute power during the test, disconnect the negative cable from the passenger side battery and connect your meter or test light like this.



It is a test light in the illustration, which will work also if your meter is suspect. The drain is likely big enough for the light to glow at least dimly. Generally, you should see a draw of 50ma (.050a) or less with the key off, doors closed and under hood lightbulb removed. Some of the computer modules will "wake up" when the battery is first connected and it can take several minutes for them to go back to sleep.

If you have no draw, go over both ends of all the battery cables and the grounds between the engine block and frame, checking for corrosion and tight connections.

If the draw is high, disconnect alternator to rule it out. If it's ok, hook it back up and start pulling fuses until meter reading drops or test light dims.

 

You should start the dvm scale on the 10 amp circuit first to avoid blowing fuses or the meter.

 

finally got back to this. found 2 problems with my meter 1) it has no 10 amp scale, highest is 200mm 2) helps when you start with a meter with a working fuse!
Got a new meter
Got the truck started ran fine for two days. I had disconnected the winch on the back, made sure each night the light switch was off Auto position, made sure heat was turned off. Plugged in. Started fine for two days.
Then accidently left heat on, NOT plugged in. The following morning completely dead.
Charged up the batteries. Disconnected 1 battery and read (Everything off), Used 10 amp scale and got 3.65. Turned heat switch on 3.79, Turned headlight switch to Auto, no changes.

According to that chart above this is about right?

 

Is that 3.65 amps or milliamps?

 

I'm on the 10 amp scale so I would say 3.65 amps

 

That is a significant draw, should be 50ma or 0.050A. Pull fuses one at a time and watch the meter. A fuse puller or needle nose pliers will make it easier. Hopefully you can identify which circuit the draw is on.