I was traveling, in Malaysia on business for a week, and I didn't bother to bring my charger. My battery has always been good for at least a week, even with extra page turns from long flights.
Right at the end of the week my reader 'locked up' overnight. The last page I read was displayed and it showed one bar consumed of battery life. I had left the wireless connection turned off to conserve power. The reader would not respond to any buttons and the power-on slider just made the red charging light blink a couple of times. The reset button had no effect. I removed and replaced the battery with no effect. I tried charging through the USB port but my laptop did not even recognize the reader when I plugged it in.
When I got home, a few hours of charging through the 5V port fixed my problem and the reader did a hard reset power-on. Phew!
Maybe my battery life indicator was way off but I've run it down every other month just to sort of calibrate it. Very odd behavior and it cost me a lot of ringgets to buy a couple of p-books for the flight home.
Moral of the story is? Don't trust the gas tank? Never leave your charger at home?