Hello, just accidently jumped in this forum, and felt like i should share my experience here too.
So i used Panasonic CF53 for couple of years no issues so far, but the battery life at some point started to feel like pain in the *ss. Came to decision to re-cell it with the Panasonic 18650 cells over 3000mah i have left from some other projects. Long story short, yes it is possible to replace all o these 9 cells and bring battery pack back to life as i did, but the problem on the way to that you're going to face is no way to properly dismantle it and put it back together nicely as the plastic cover is really thin and difficult to work with.
So in the end of the day it looks like kind of Frankenstein but gets the job done very well. P.S. who's gonna see it except you it's under the cover.
GOOD LUCK ;)