I was reading, and half way down a page my kobo touch just turned off and wants a charge. Why was there no warning at all?

I only have the one charger cable because microusb isn't common enough yet. I have millions of mini usb cables at work. It's going to be a long bus ride home...
Please make a battery icon on the bottom or top of each page optional, at least when it is getting low. Preferably all the time. It would only need to update when the page is turned. I would love to have the time too, even if it only updated with the page turn.
Thanks for the frequent updates though
Chris.