Although Rafe and I have had the Nokia N8 for close to a month now, neither of us has got round to disassembling the bottom to test removal/exchange of the BL-4D battery. Partly because there's a question mark over whether this does in fact void the warranty, but mainly because the battery life is so good that neither of us has missed not being able to swap cells. In any case, Micky Aldridge has gone where we feared to tread and I've embedded his video below, showing removal and replacement. Looks like a 5 minute job at most, should your N8 battery ever degrade or fail.

Note that Micky refers to pulling the battery because of problems. As noted in the comments below, this isn't really necessary, as there's a hardware button fail-safe power-off, analagous to on any PC or Mac computer.

(via The Nokia Blog)