
When I first received my T-Mobile G1 the battery life was excellent for the 1st 2 weeks. I then began to notice that the G1 was draining very fast, so I disabled Wi-Fi, and GPS thinking that would help, it didn't. I started looking around to see if other G1 owners were suffering the same problem. I came across this Android Community thread and found out many G1 owners were suffering from the same problem.
I gave T-Mobile customer care a call and explained the situation. I told them the 1st 2 weeks I had the G1 the battery was excellent, but now it hardly made it through a day. The rep told me that T-Mobile is aware of the issue of the G1's battery draining fast and that they were working with HTC on a software fix. The rep said she would send out a replacement battery, and to keep the original as a backup.
I received the new battery, it seems to be working better than the original. The battery looks identical to the original. The only difference I can tell is the new battery is listed as part # 35H00106-02M, the original battery is listed as part # 35H00106-01M. They both have the same "hTC INNOVATION" logo on them.

Hopefully an update will be released soon to fix the issue.