Don't know, honestly. How many hours on a week-long trip do you spend with your Kindle turned on? THey're claiming the iPad will go a month on standby, so when it's turned off, there shouldn't be an issue with battery drain. But with sifi off (I'll assume there's an option for that) and doing nothing but reading, I don't know how many hours of operation you'd get.

I suspect the answer is "a lot less" than the Kindle, since the iPad uses an LED screen, which is going to drain the battery faster than an e-ink screen.