Battery drained by faulty SD card/reader
Going by other's reports of good battery life, my Kobo Glo battery wasn't lasting as long as it should have, but I think I have found the cause of the problem:
I had a 4GB card in the Glo's micro SD expansion slot, and I was getting about 8-9 hours reading time with WiFi off. It didn't seem to matter whether the book I was reading was on the external card or not.
Yesterday I replaced the Glo's internal 2GB card with an 8GB one, and removed the 4GB card from the expansion slot. (I did this because images were not being cached properly for books residing on the external card, greatly slowing the display of thumbnails). Since then my power consumption appears to have dropped dramatically.
It'll take some time to work out exactly how much it has changed, but based on the last day's use I might now get 30 hours or more reading time per charge.
I can't imagine it is normal for a micro SD card to use so much power, so I guess either it was a faulty card, or a fault with my Glo such as a short-circuit in the card reader. I'd need to buy another card to test which.