When I installed the original one that was linked here I did notice battery issues. The app was always active even though I never launched it. I ended up uninstalling it because I wasn't using it and then my battery life went back up. I just upgraded to the latest OS which comes with Messenger but I didn't install it this time. Maybe I will though and test the battery usage again.
Current: AT&T 8300 w/Plantronics Discovery 640
Previous: Nextel BB7520 w/ Plantronics Discovery 640