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03 Duramax with Allison. 2500 HD crewcab, 175,000 miles.
always serviced, tires rotated/aligned. Only tow a 21 foot bass boat locally 5 or 6 times a year.
2 weeks ago i tried to unlock doors with key pad but locks wouldnt disengage.
Opened door with key & all electrical was dead.
Connected battery charger & it pegged the charge side.
Batteries were almost 6 years old.
Next day they were charged enough to drive to get new batteries.
drove local about 300 mies in the last 16 days.
This morning same secenerio , all electrical dead, battery charger pegs on charge.
Took altenator to 2 different parts houses today & it tests good.
Any Ideas whats going on ??
 

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This morning same secenerio , all electrical dead, battery charger pegs on charge.
Took alternator to 2 different parts houses today & it tests good.
Any Ideas whats going on ??
After you get both batteries charged back up disconnect both negative battery cables. Make sure nothing is left on, pull the hood light out. Then take a test 12v test light and connect between one of the ground cables and the (-) post on your battery if any thing is draining your batteries the tester will light. Pull fuse's until you find your drain also it's possible the alternator has a blown positive diode which will drain your battery. Disconnect the 10 ga. at the back of the alternator if the light goes out it's the diode.
 

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My 07 LBZ does the same thing, i unhooked my altenator, yesturday, and this am my batteries are up. I'm hoping that its my altenator.
 

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A likely culprit on the LB7s (maybe the newer ones too) is the glow plug relay. I had an 04 that gave me problems. Turned out the relay for the glow plugs was stuck closed, so my batteries would completely drain in under 20 minutes.

Any idea how fast it drains? Are you good with a multimeter?

First step would be to check some of the likely suspects, and I'd vote this one up there for sure, as far as common problems go.

Failing that, set the multimeter (or ammeter) to read current. Hit me up if you need more help.
 
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