Hello Jimcooper,
Page 170 of the XF100 manual specifies both the built-in rechargeable lithium battery (aka, the back up battery) and a CR2025 lithium button battery. One might interpret that particular section and page in the manual as referring to the same battery, but it actually refers to two different and distinct batteries. I apologize that it might be easily misread as being otherwise.
The built-in rechargeable lithium battery (aka, the back up battery [which runs the date/time/settings]) is the one we're referencing when referring to your inquiry. It's internal and cannot be changed by the end user as it requires Canon Factory Service to do so.
This stands in contrast to the CR2025 lithium button battery (which we supplied) runs the XF100's wireless controller. This is not the same as the built-in rechargeable lithium battery that's referenced when we talk about your direct inquiry. You can change out the CR2025 lithium button battery on the wireless controller as needed.
Given this information we're unable to suggest attempting service yourself and would instead recommend using the Canon USA web site (linked here) to set up a service ticket for the camcorder to be sent to Canon for evaluation and/or service.
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