Was 4 NiCAD cells in series, likely 1.2V each, so not quite 5v. Instead of doing that, you could run a pair of wires outside of the case and attach it to a 4 pack of NiCADs. If they leak, they're external and won't damage the Lisa.
I've done similar things with the weird Lithium battery that's used by newer macs, that small tiny weird motherboard battery that's on powermacs and similar, I used alligator clips and ran the wires out the back to a AA holder that had enough Lithium Ion batteries to match the voltage, but in the Lisa's case, you'd want NiCADs.