I have a PowerBook 140 that — apart from a dead screen requiring the inevitable capacitor replacement — seems to work well. It has no battery, though, and any available battery will likely have 25+ year old NiCd cells.
What I'd like to do is build a replacement battery pack with modern cells in a 3D printed case. I'm aware that the Apple originals had some kind of sensors in them, but they look fairly simple. What I can't find, though, are dimensions so that a replacement pack will fit snugly into the battery bay. I guess I could spend some hours with digital calipers, a notepad and much swearing, but drawings and schematics would be ideal. Where might such documents be?