That’s exactly what I’ve done, you just have to squeeze the clip at the end of the slider with a pair of small pliers to get it to slide off the battery. Then, I found a piece of double sided tape (the thin kind) applied to the bottom of the ‘hole’ (the lower casing) works to keep the front panel (as you can now call it) in place - it otherwise tends to fall off.
My current project is to design a very simple battery replacement - six AA NiMH cells. They run the PB100 for a reasonable length of time with a good run-down gauge/warning and, if the PowerBook adapter is plugged in, they don’t cause any problem, though they don’t charge properly either.
To charge them, I have a circuit with a USB-C socket. If the socket is accessible externally, this may also achieve the result of running the PB100 from USB-C (handy for people without a working original adapter), though there is still a small issue of voltage (while charging, it’s 8.4V) to be worked through. I decided this was still simpler than the Li-ion split-cell charging arrangements pioneered by Alaska360 (I think it was) but ultimately I’ve run into the same problems, just without bothering to solve them properly
I’m happy with the lower cost, the possible ability to ship without battery cells for overseas sales, and I think I’m even possibly OK with the compromise of only being able to charge the battery external to the PowerBook. It’s only for a bit of fun, at the end of the day. I’m also designing it to accept 12 cells for a longer runtime, though I’ve yet to find anything to do with the PB100 that takes longer than a couple of hours (which six good 2300mAh+ cells provide). I understand the original battery was also about 2.3Ah.