Battery discharge trouble. Need advice

[PackRat239]

Thanks to all you guys help, my 93 F250 7.3 runs great, but... I have a battery drain that kills the batteries overnight. Batteries test good, alternator also test good, (new Alt), New Battery Positive cable. I have tracked the drain to 13, that powers the RABS system, brake lights, flashers. If I remove that fuse, batteries do not drain. Even after 5 days. I have unhooked the brake light switch, still drawing, disconnected the harness for the rear lights, still draws, Could the rabs module behind the glovebox drain the batteries, as it has power at all times? Where else should I check? A new module is not real expensive, but I hate to change out workink parts.

Thanks,

Dale

 

[franklin2]

Sounds like you are on top of it and have good troublshooting skills and ideas. So just unplug the RABS module and then see if the drain goes away.

If you don't want to wait 5 days, take the negative cable off the driver's side battery and sit it on a rag. Then take the negative off the pass side battery, sit it on a rag also, but take a testlight and clip the alligator clip to the terminal sitting on the rag, and stick the probe onto the negative terminal of the battery. If the testlight glows bright, you still have the drain. Then you can unplug stuff till the light goes out.

 

[justinray]

*** I had the same EXACT problem. It was trailer wiring being grounded/shorted. Irs the same fuse.

 

[PackRat239]

Thanks for the reply, that is how I test for a battery draw too.

 

[PackRat239]

Thank You, I will look into that. I checked all the wiring from the cab to the bumper and all the harness looks fine, except for a lot of crud inside the plastic covering. I will look closer. My truck did not come with a seperate trailer harness that I can see.

 

[PackRat239]

OK, same problem, new question. I am pulling my hair out chasing a battery drain, and not eliminating it. QUESTION: If one battery is good and one possibly bad, will the bad battery drain the good battery???

 

[justinray]

If it is grounded internally, yes. Like if the plates collapse, etc, yes.

 

[PackRat239]

Thanks for the reply. Here is what is happening. I have tracked this draw down, removing the seemingly offending items, and had no draw with one PS battery used as test and DS battery unhooked. When I went to hook up DS battery, I got a spark. So I hooked up test light and had a major draw now!!! Pulled EVERY fuse and breaker, and still had draw. Decided to charge batteries, hooking charger to PS battery made test light go out on DS battery.??!! Any ideas? I am ready to jump off the roof over this problem.

Dale

 

[The Warden]

Yeah, especially if you don't know the history behind the batteries, I would go ahead and replace them both. Sounds like there's an issue one way or another...

 

[franklin2]

You can take them out or get it over to a store that tests batteries for free, and get them tested. Their tester puts a load on them and checks them that way. Putting a meter on them is not a good test.

But it sounds like you are right, you may have a bad battery. I know it's expensive, but batteries in parallel like in these trucks work as a team, and they should always be replaced as a set at the same time. As you have found out, when batteries are paired together, both are only as good as the worst one of the pair. A brand new battery paired with a old one will only be as good as the old one.

I had this same problem, and found I could actually run the truck on one battery, leaving the bad battery out till I gathered enough money to buy two new batteries. It was summertime though, I am not sure one battery would get it going when it's cold outside.

 

[PackRat239]

Thanks guys. I already had them tested and one is bad, one is good. Will replace as a pair. Just want to be pretty certain that I have found the issue before putting out the cash on new batteries and having them get drained too.

Dale

 

[icanfixall]

Heres the deal with dual battery banks. Lets say you have them is for 3 years and one goes bad. So you replace the bad battery. Now there are one new and one old battery. Both have a full charge but heres where it gets interesting. The old battery is going to pull down the new battery to its level of charge and capasity. Think of this as two cylinders filled with water and a line connecting both together. If the level drops in obne of the cylinders the other will pull from the full one to "even it out". Thus draining down the good full battery. If we could install a breaker between both batteries when they are not used then we could isolate bad batterys. Its a tuff bullet to bite but replaceing both at the same time works better in the long run. I know semi trucks have banks of batteries and many wont change all of them if one goes bad. We have to do what works for us ...

 

[franklin2]

Its a tuff bullet to bite but replaceing both at the same time works better in the long run. I know semi trucks have banks of batteries and many wont change all of them if one goes bad. We have to do what works for us ...

Your right, circumstances are not ideal sometimes and you have to mix batteries, but if you can afford it, two new ones are best, whether it's a diesel pickup, a semi, a golf cart, a solar system, etc. We are talking many many batteries and $1000's on some of these systems when the batteries go bad.

 

[PackRat239]

icanfixall,

That was what I was thinking, too, but I wanted to be sure. Thanks for the info.

 

[PackRat239]

At least it wont be thousands for me.