I've had the same thing happen on my T1 twice over the last month. Your's may be a different issue and I still haven't confirmed this, but my suspicion is that the wireless did not turn off automatically for me, even though I had put the reader into sleep mode and this drained the battery overnight.
On the last occasion (& I can't remember the first time), just before putting the reader down for the night, I was trying to connect to the internet but gave up after the reader took too long to connect. So while it was trying to connect I cancelled the connection and continued reading. Woke up next morning and the reader's battery was flat.
Having a later play with this I noted that even when I cancel the reader trying to establish a wireless connection, it continues to try to. What I haven't checked yet is whether or not it then shuts the wireless down automatically (which it normally does do when I am connected and go back to reading).
Has anyone else noted this?