Volkslogger Battery?

I've got one of the newer Volksloggers, with the rectangular connector
(hardware version 3.4, firmware version 3.6). No operating problem
with it, but I have a preventive maintenance question on the 10 year
old device.

Old messages on RAS mention the presence of an internal battery, and
say it's described in the manual. But my manual (edition 1.7.2, for my
hardware and firmare) does not mention an internal battery at all.

However, searching the web resulted in a recent NTSB report that shows
a photo of a Volklogger of my exact hardware version and firmware
version that clearly does have an internal battery, which NTSB says
is "to maintain clock operation (and possibly presets)."
http://www.ntsb.gov/Dockets/Aviation...317/430945.pdf

Is my manual just plain deficient? If my Volkslogger really does have
an internal battery, what will I experience when it runs out of juice,
how long should it last, and who can replace it?

-John