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Slow battery drain diagnostics

High Five H2

Well-Known Member
Messages
1,574
Location
West Texas
Ever since I've owned my H2, it's had a slow-ish battery drain, and I'm trying to diagnose it.

Some background -

  • The PO used it as a search and rescue truck and it had a lot of electrical stuff added on. I've taken off everything aftermarket that I could find, and there's nothing attached to the battery.
  • I took a multimeter to all the fuses, inside and out, and none of them consistently show a draw.
  • It's about 3 amp/hours (right?), so if I leave it for 2 weeks it will be dead.
  • There's an aftermarket alarm, but turning it off or removing the fuse doesn't affect the drain.
  • Occasionally, I'll get a 'service charging system soon' message and a red battery warning light. It typically comes on when I'm parked or sitting in traffic for a long time and it always goes away when I start driving.
  • If I drove it frequently, I wouldn't notice the drain at all.
  • I put a new battery in a few months ago and if I drive it regularly it stays charged all the way.
  • Autozone tested it and said my battery and alt were both good. I don't know exactly what they test for other than total output.

I have a theory that the alt has a bad diode and it's allowing the battery to drain, and that's why the warning light comes on. The drain is bad enough at low RPMs to trigger the light. I'm going to test it now, but if anyone has any other suggestions, I'm all ears. I also have an upgraded replacement alt so I might just put it in and check the draw.

Thanks everyone
 

Iwillnc

Well-Known Member
Messages
232
Location
NC
Have you checked the connections on the battery/alternator/starter to be sure they are clean?

From what your saying I doubt it is the problem but the most common source of H2 drain was always the Onstar system it would randomly draw even long after the truck was shut off. Even my truck began drawing several years back and without touching anything else I pulled the Onstar fuse and my problem was solved.

If your truck originally came with air suspension and it’s been removed make sure there are no loose grounds hanging around the back.

Check body to frame/engine to frame grounds for cleanliness and tightness make sure they have a good connection - the typical.

Honestly if I were you I would replace the alternator as it may be an issue with the internal voltage regulator going bad. Easier in your driveway than getting a DIC message your truck isn’t charging several hours from home on 95 and having to quickly find a auto parts store before your battery was too weak to power the truck... not that I know from experience or anything...
 

High Five H2

Well-Known Member
Messages
1,574
Location
West Texas
Have you checked the connections on the battery/alternator/starter to be sure they are clean?

From what your saying I doubt it is the problem but the most common source of H2 drain was always the Onstar system it would randomly draw even long after the truck was shut off. Even my truck began drawing several years back and without touching anything else I pulled the Onstar fuse and my problem was solved.

If your truck originally came with air suspension and it’s been removed make sure there are no loose grounds hanging around the back.

Check body to frame/engine to frame grounds for cleanliness and tightness make sure they have a good connection - the typical.

Honestly if I were you I would replace the alternator as it may be an issue with the internal voltage regulator going bad. Easier in your driveway than getting a DIC message your truck isn’t charging several hours from home on 95 and having to quickly find a auto parts store before your battery was too weak to power the truck... not that I know from experience or anything...

I'll check the battery/alt connections, that's a good idea. I took the fuse out of the onstar system already. I don't know if the air system is disconnected or not. It has a 6 inch lift but there are air bags inside the rear springs, so i'm not sure. but the button does nothing.

I need to do this alt soon, i just haven't gotten around to it because i'm lazy.
 

High Five H2

Well-Known Member
Messages
1,574
Location
West Texas
I got the alternator replaced tonight, finally. It was one of those aftermarket 250 amp ones so it wasn't a direct fit. I've just driven it around for a few minutes but it's working right and maybe this is just wishful thinking or placebo effect or whatever but it seems to run a bit smoother. I'm going to let it sit or test it to see if there's a drain now, or just continue doing the wishful thinking thing and hope it's gone until I have to charge it again or not.
 

High Five H2

Well-Known Member
Messages
1,574
Location
West Texas
Well, I finally gave up trying to fix it myself and took it to a stereo shop. They did a big-4 wiring upgrade and checked out the leak. The guys says its pretty normal for an H2 and that if I can go 3 weeks without starting it I'm doing pretty well. So, problem solved, I guess?
 

Exodus

Well-Known Member
Messages
49
Location
Alaska\Philippines
Well iof your H2 has onstar in that like the H3 does ?? that is what is causing the slow battery drain

most just pull the fuse for it and problem solved
 

High Five H2

Well-Known Member
Messages
1,574
Location
West Texas
I think it does have on star, but I can’t remember. I have a vague recollection of reading about onstar and pulling the fuse but I will check again.
 
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