Battery Drain in 2004 H2
 

Recently replaced the battery after vehicle having not been used for a month. New battery has drained in as little as 30 min. Has also not drained in 4 hrs. Removed Radio fuze, seems to have solved problem in that battery holding charge for 3 days now. The question is: What is the next step? Does one replace the radio, or is the problem in some other part that is powered through that fuze such as relays, modules, etc, and how would that be determined? Frustrating is it not? Thanks, in advance, for your input.

is it an aftermarket radio or stock?

My 2003 did the same, it was the electrical portion of the ignition switch. It was not turning off the acc function on the switch. So even though the key was off and pulled out the ignition was still on. It was a simple and cheap fix once I figured it out.

OP just recently fought with this particular issue on my 08 H2. Mine was draining within a couple days not over night though. Also my issue was fixed by disengaging the ONSTAR Fuse. several guys on here pointed me in that direction and I did multiple parasitic tests as well. Hit up YouTube for a better understanding of how to do a correct Parasitic Test it was very helpful in determining what was causing the issue hope this helps and good luck. As stated im sure above make sure you disconnect any aftermarket wiring that's installed as well if possible to confirm those are not causing you issue.
Again Good Luck
Mudd

Hmm that's an interesting thought. On the 03-07s does the cig lighter stay on all the time? Mine are always on even when the rig is completely off.

To Hummer on Fumes: Radio is stock.