A while ago there was mention of T-Mobile upgrading the Google Android T-Mobile G1 battery with a longer lasting replacement, well apparently its happening.
Apparently a G1er got off the phone with T-Mobile and posted this at Android Central…
Just wanted to let you guys know that i just got off the phone with a tmobile supervisor who confirmed that replacement batteries are being sent out and that there was an internal memo sent around that extra batteries are being sent out free of charge and there will be no need to send back your old one! He was unable however to confirm whether or not they would be of a higher capacity or not.
So there you have it, great news for T-Mobile G1 owners.
Source — android central