If the internal battery needs to be replaced, it's supposed to be done by a dealer. See p.58 of the manual. ftp://ftp.panasonic.com/pub/Panasonic/Drivers/PBTS/manuals/AG-HPX170_oi.pdf
It's a lithium button, so it should charge itself and keep time for a decade or more, as long as you use the camera once a year or so.
Thanks very much for your timely reply and information. My camera is still ticking along. However, I don't use
it as much as I did in the past. I have only logged 86 hours on it. I purchased it new back in December 28, 2008.
I will check out the link you've provided as well as use it soon.
Note that the internal battery is charged only when you power with the battery eliminator plugged into the cam. This cable Assy plugs into the battery charger.