Hi guys, I don't know if posting this is stupid but here we go: I bought a couple of N900 (one for me and one for my girlfriend) and Nokia gave us two additional batteries for expending 1000 pounds. The thing is that I used the device for a couple of days without problems with the original battery. After that time I tested the free one and I got some unexpected reboots. My girlfriend told me "It has to be the battery". I told her, that doesn't make any sense but I changed it. After that I haven't had any more reboots. One week usage now... Maybe it's worth to try? Good luck to everyone.