A friend of mine has a Canon Rebel XTi, and it died. He says the battery is charged, and it hasn't gotten wet at all. It worked the other morning, then 2 hours later- nothing. No error code, no blinkies, just nothing.
All I can say is I had something simelar I thought my camera (550d, is that XTi?) was dead, but it was the sd card slot cover that wasn't closed properly, the the camera did nothing at all, nothing on the display even I think. Closed the cover and everything was fine again.
I would try a known good battery. I had one go bad for my 5D after using it. I used it and then recharged it but nothing happened when I put it in the camera. It seemed to charge fine, the light blinked like it was supposed to, and then went solid. When I got around to using it again, nothing, notta, zip. I thought my camera was dead. I put another one in and it was fine. Put the bad one back in and nothing. So I put the bad one back on the charger and it blinked for a few seconds and went to a solid charged light but when you put it in the camera, nothing.
I have fond memories of the XTi, having taken one to Europe in 2008. Is your friend using the original battery? The Xti dates from 2007. A five or six year old battery is bound to croak as normal life is 2-3 years. I've had batteries barely last one year.
If there is any reason to suspect the battery, they can be had on ebay really cheap. My XTi went out on me a year ago, and a new $5 battery was all it took to get it going again. It still takes several hundred shot between charges.
