Did you check for a draw with the test lamp like I showed you?

I think its time for some new batteries Stanley.

Disconnect the negative cable. Clamp the test lead to the negative post on the battery, then probe to the negative cable, which will be disconnected. If the test light illuminates, you have a draw. Then start pulling fuses until the test lamp goes off. That will help narrow it down.

If no illumination, no draw. or at least not a big enough draw to kill the battery like it is. Either way, the batteries were stamped Jan/09. 5 1/2 years old, they are prob done anyhow. :bong:

in most case's if factory installed dual batterys one battery goes to the starter and the other one goes to a solenoid to keep the lights from dimming..this would be called the plow package..if they are tied together like a diesel then it was most likely done after market like i did to mine..most likely a bad battery taking out the good one..

Got 2 new Interstates, lets see what happens..

thank you for the replies.

the test light worked ok on older cars,newer cars and truck could show a draw for a while until all the modules go to sleep,
the best way to check a draw is with a DVOM set on amps,it might read high at the beginning but after a while (up to 20-45 minutes)it will drop down,rule of thumb is anything under 20 milliamps is ok, be careful not to turn on any accessory's you might blow the fuse in your meter

I recently traced down a parasitic drain on a 2005 Ford using the test light method. It had an aftermarket radio, which must have been shorted internally. Unplugged the stereo harness and test lamp went off and no more dead battery after sitting for 2 days. Your way is better though....Most of the stuff I have is still from the cassette player days !