Battery Drain?

[Hans3T]

My battery went bad about a month ago, and they replaced it under warranty; however, this new battery has a slow drain I think. The other day (after about 6 days of inactivity) I went to start Barney up and the new battery was dead. We jumped it and I went to start it after 3 more days of inactivity and the battery sounded very weak, but it did start.

Does anyone have a way to determine what might be causing this problem? :huh:

 

[f5moab]

Only way I would trust is via an ammeter but most home ammeters cannot handle current over 1 (or 2) amps. You can install a shunt by using a 1000 ohm resistor between the battery cable and the battery, and then jump across the resistor with a voltmeter. The reading x the resistor rating will be the amp draw.

Once you see a large amp draw (above about 55 milliamps, start pulling fuses till the draw goes away. MAKE SURE THE VEHICLE HAS BEEN OFF FOR OVER 20 MINUTES. THE FIRST 20 MINUTES HAS THE COMPUTERS STILL WIDE AWAKE; AFTER 20 THEY GO TO SLEEP.

Oh, and after all that, just a note; not all new batteries are a-ok. A new battery can be worthless as an old battery. So, you can also try and see if a nearby auto parts store can test your battery.

 

[4speedfunk]

Hey Hans. Have you added any electrical accessories? Check those first. I saw your post with all those under-side lights...look for a pinched wire somewhere. Losing voltage like this points to a non-fused short somewhere, or a device that is left "on". The biggest non-fused circuit most of us have is the winch. Check the main feed to it and also check to make sure the winch controller isn't "controlling" without you knowing it.

Also, as strange as it sounds...check your brake lights. Most brake light switches are fed from a constant 12v source for safety reasons. Getting out of your truck and walking away can lead to a dead battery simply because the brake lights are on. I've had cars in the past that did this...and I didn't notice because it was daylight. Brake lights aren't subject to "ding-dong" alarms like your headlights are, so its very easy to not notice them as you exit the truck. The H3's brake light switch (down by the pedal) is known to stick "on". Mine was sticking when brand new, and it was replaced by the dealer.

 

[Hans3T]

Doug, great info. I had no idea the computer stayed on that long! Interesting. I will have the battery tested at Advance this weekend.

CJ, as common sense as checking the new undercarriage lights is....that may have been my saving grace. I went ahead and checked all the lights, and they were off...HOWEVER, the "brain" motherboard/control unit for them had two small LEDs that were on. I guess somehow I had not shut the unit off all of the way... So, while you would not think two teeny-tiny lights would be the problem, you never know. If it cranks right up tomorrow than I think we have a winner.

I'll post-up how it goes.

 

[f5moab]

Did not know you had undercarriage lights. And I might add, it is computers; PCM or ECM/TCM (if auto), BCM, EBTCM, TCCM, SCWS, SDM I think that's it.

 

[Hans3T]

Well the truck is dead again... There has to be a slow drain somewhere I'm guessing. Since the undercarriage lights I hardwired to the battery are the newest mod, I'm guessing its them causing the trouble. Does anyone have experience with a battery "brain" that cuts off current? Or any other suggestions? I'm awfully frustrated.

 

[alrock]

Why not disconnect the undercarriage lights for a while? But I think the "brain" you are seeking is the one between your ears as you hold the multimeter in your hands

 

[Bigunit]

Why not disconnect the undercarriage lights for a while? But I think the "brain" you are seeking is the one between your ears as you hold the multimeter in your hands

Good advice Alrock. Reminds me of the old joke: The patient says, "Doctor, it hurts when I do this." Doctor says, "Then don't do that!"

 

[LagunaH1]

Also: How often and for how long do you run the truck vs. how long it sits at home? Charging the battery can take longer than what one might think. 2nd edit: If, for example, you have a bunch of accessories that, together with the truck itself, comes close to the max output of your alternator then there will be very little left to actually charge the battery.

Edit: Do you have a ScanGauge hooked up to your OBDII port? It comes in real handy because you can use it to measure the battery voltage at any time without having to turn the truck on. It might be interesting to observe what the battery voltage is when you get home from a drive (ideally it should be 12.5 volts with the engine off) and then see how quickly the voltage drops.