My truck was sluggish starting one day and I thought it was because it had sat for 3-4 weeks. I ran it and topped up the batterys. I went to start it a week later and the batterys were so low they wouldn't start it. I boosted it and ran it for about 1/2 hour then shut it off and put the charger on it. It charged 5 amps for about 1 hour and then dropped to nothing. I thought this was strange if the batterys were dead so I concluded one or both batterys must be bad. I was leaving on a road trip the next morning so I bought 2 new batterys and installed them. The second morning on the road starting seemed sluggish again. When I got home I put an ammeter on each of the battery positive leads. One showed about .5 of an amp until the interior lights shut off then went to zero. The other has a constant 1.6 amp load on it. I checked for lights on everywhere and can't see any on. Anybody else had this happen? I am new to diesels and have heard of glow plug relays sticking on. Is this possible?
Brian

I have not heard of the glow plug relay and I am sure that they pull more than 1.6amps. My opinion would be to start un-plugging stuff that you added. Like the brake controller. Is there an air pump for the airbags? Surely something is plugged in or maybe not wired correctly and staying hot all the time. Good luck keep us posted.

Aren't the 2 batteries simply in parallel in the Duramax equipped trucks? I don't believe there is a battery isolator used between them. So if you were seeing a 1.6 amp draw from one battery and none from the other, the one showing the 1.6 amp current flow is the "good" battery continuing to charge the other battery until the voltage level between the two equalizes.

I finally had some time today and checked out some things. The batterys are in parallel and I couldn't figure out why the 1.6 amps was coming off one battery and nothing off the other. I finally found I had a crappy clip-on DC ammeter and in the position I put it in to get to the positive lead it showed 1.6 amps. When I took the positive lead off the battery it still showed 1.6 amps. So I don't seem to have something discharging my battery and when it failed to start it must have been because it sat to long and I never got it charged fully before I let it sit again for a week. I still can't figure out why the batterys didn't take a charge when I put the battery charger on them. Maybe I have a crappy battery charger also!
Brian

Have you chked the charging volage to the batteries with a multimeter?
I would not trust the volt meter in you truck. If you have chked this what was the reading. I believe you should be getting 13-14 volts at the battery. Also chk the amps that are drawn during cranking for startup. You could have a bad starter killing your batteries

Mine sits for a month at a time and it fires right up

sounds like you need two new batterys.

sounds like you need two new batterys.

He bought two new batteries. Did you read his original post?

I will check the alternator output to make sure the batterys are being charged by the truck. Checking the starting current is also a good idea. I left the batterys today at 12.72 volts. I will see if it stays close to that voltage in the next few days. Thanks for everyones input.
Brian

Check your grounds.

I've found if my truck sits for more than two weeks the clock radio memory will draw enough amps too drain batteries. Solution was to buy a cheap battery minder.

I've found if my truck sits for more than two weeks the clock radio memory will draw enough amps too drain batteries. Solution was to buy a cheap battery minder.

How did you figure out it was your clock?