98 1500 5.2 Mystery Battery Drain

[Charles Waters]

Good morning all...

I have a 98 Ram 1500 Laramie that continues to drain the battery while sitting.

After 3 or 4 days, the battery is low enough that I can't start the vehicle unless jumped, or I always end up having to leave the battery charger / maintainer connected.

Recently, the Alternator and PCM were replaced. The battery was replaced about 8 months or so ago (Autozone Duralast), and all has been well until maybe 4 months ago.

When I take it to Vatozone and have them do their cheap little load tester, they always come back and say the battery is good, but the Alternator is bad. Even before the new Alternator, I got the same results from them.

I went to Interstate Corporate store Monday, and they still have one of the OLD SCHOOL dial load testers. When the dude put it under an extreme load (turned the dial to 12v like it was cranking), the battery dropped to 9.61 (9.60 is the limit), then when he backed the load off, the battery recovered back to 12.67 volts in a couple seconds, which is where it was when he started, with the truck powered off, sitting in the parking lot.

So I decided to do a Parasitic Test on the battery, as well as take some pictures of what the output from the Alternator is. I'm hoping that y'all can help me narrow it down to if it is still a bad Alternator, or a bad battery.

Parasitic Test Results. I even pulled the IOD fuse, and there was no change on the amperage. I tested all the fuses that I could, and they are all 0.00mw.


Then after starting the truck, I put it in Reverse, Headlights On, Max A/C, and this is the result at idle:


Then I left it in Reverse, Headlights Off, A/C Off, and this is the result at idle:


Then I put the truck in park, Headlights On, Max A/C, and this is the result at idle:


Then I left the truck in park, Headlights Off, A/C off, and this is the result at idle:


To me, these results seem a bit on the low side for the alternator output. Especially when under full load at idle.

When the truck is off, battery full charged, the battery is showing like 12.7/12.8 volts when fully charged. Even if I disconnect it from the truck when charged.

What do you all think?

 

[Doughboy43]

A good fully charged battery should show between 14.0 & 14.7 with no load so it could still be the battery. Test it with it fully charged and unhooked to get a true reading. There is chance there's a bad dioad in the alternator, I've only ever bench tested for that and it was a while ago. I do know dioad's are hard to diagnose. Charge it with a battery charger to make sure it's fully charged, I like to use a slow charge when I do it.

 

[Charles Waters]

I did that over the weekend. On Friday I believe it was, I disconnected the battery from the truck (completely), and threw my 2amp charger / maintainer on there.

It showed fully charged in about 4 hours after plugging in the charger. Even when it's down to like 10volts, it seems to charge extremely quick, compared to other batteries I have had go dead, where they take 6+ hours to completely charge.

I left the charger on it hooked up in maintenance mode over night, just to be sure.

It never got about 12.87v when sitting. I checked it connected to the charge after full charge. And after disconnecting the charger, giving it a couple hours, it tested like 12.62v, and stayed right in that area until I hooked it back up to the truck and started driving it around.

 

[Charles Waters]

A good fully charged battery should show between 14.0 & 14.7 with no load so it could still be the battery. Test it with it fully charged and unhooked to get a true reading. There is chance there's a bad dioad in the alternator, I've only ever bench tested for that and it was a while ago. I do know dioad's are hard to diagnose. Charge it with a battery charger to make sure it's fully charged, I like to use a slow charge when I do it.

So the truck has been sitting in the driveway since about 2pm yesterday afternoon.

I did a couple things tonight, and I'll check again in the AM. I disconnected the battery from the truck, and this is the reading my DVOM gave:


I then went to my Charging System tester. And this is what I got. Now remember, last week I said the truck was completely dead! It was showing "Replace Battery", but it also 4 or 5 days since I started the truck, and the battery was so dead, the dome lights didn't even come on. I only put about 30 miles of freeway driving on my truck, and it was clearing stating to replace the battery. Current results this evening (after Sunday evening - yesterday on the charger/maintainer):



When I ran it over the weekend, after driving the 30'ish miles back home at freeway speed (around 2.5K RPM), it showed measured CCA was under 400, SOH was about 45%, and SOC was about 68%, and the resistance was almost 9.2.

I will double check it in the AM (or later this evening), and post the results then.

 

[Doughboy43]

Looks like a power drain. I had a vehicle once that I finally traced the drain to a power seat switch that didn't work and had to test the switch to find it. Really had me scratching my head over that one, wouldn't have found that if not for a tec I know having a similar issue. Was the parasitic test with the battery disconnected?

 

[Bill Blackmon]

IHad a parasitic drain a few years ago snd checked everything I could think of. Through dumb luck I found out the glove box light was staying on and after several days of sitting the battery was drained so low it would barely start.

 

[Keifus]

If you have a OBD reader for your truck and a android phone you can try. Car Battery Tester (obs2 & elm327. Or give this a read. How to diag car electrical problems

 

[Charles Waters]

I completely forgot to post an update... So took it to an Auto Electrical place here in AZ. They said the issue was within the harness between the ECM and fuse block(s).

While they were at it, they said the ECM and Alternator both were bad. Those two items were just recently replaced by another auto repair facility. They said the Alternator diode pack if I recall, was the culprit for that. They also said the ECM was "shutting the charge off too soon".

Warrantied both the Alternator and the ECM through the original place and the electrical folks put it in, and programmed the ECM. Ever since then, no issues with the battery draining. I have left it unplugged as much as 8 days without starting it and it cranked right over. Also now stays around the 13v genre when charging, where before it was dropping down to *low* 12v.

Thanks to all who assisted on this.