RTC battery for my laptop
 

Does anyone happen to know where the RTC battery is located in a Toshiba laptop - the model type is Satellite Pro 5100.

I've turned it upside down and removed all the panels. Underneath one of them there's a round metal thing that looks very like a NiCad or Lithium Ion battery but I'm not 100% sure. It's covered by a sticker saying "Warranty void if removed". I can't think why replacing a bettery would void the warranty (the laptop's well out of warranty anyway - but that's not the point).

The manual gives no clues, except to say that the RTC battery should only be changed by a Toshiba dealer. This also suggests that the RTC battery is somewhere inaccessible.