Whilst this is a photo copy, and some of the pages are a little askew, it was all readable and intact. A real bonus finding an old manual for a classic piece of kit that no other site had.
It was easy done, and I got exactly what I was looking for.
Text excerpt from page 24 (click to view)
Connecting a Power Source
To insert the battery pack
You can insert or remove the battery pack without turning off the computer when your computer is connected to the AC adapter. Before inserting or removing a battery pack, close the cover. 1 Move the lock lever on the bottom of the computer to the UNLOCK position.
Align the grooves and tabs on the battery with the tabs and notches on the back of the computer, and then slide the battery toward the computer until it clicks into place.
Inserting Battery Pack
Slide the lock lever into the LOCK position to secure the battery on the computer.