I have had several old T3's over the years that were terribly fussy, had to try over and over again to re do the firmware update. In about 75 percent of the cases I was finally able to get it to take can stress the battery faking you out issue, I have had remotes that seemed to work fine with a new battery installed but would not allow an update, replaced the battery with a new new battery and the firmware updated perfectly. T3's are really picky about stable battery amperage