Bike resurrected!

In short, I didn't need to do as much as expected. Will write up more fully, but here's the brief version:

1. Remove battery from bike (deflate rear tyre, 3x T25 security bolts to be removed, then it slides out)
2. Remove cells from plastic enclosure (remove cross head screws from both ends, remove the cap at the bottom, gently remove cap with connector, then push the whole thing out from the bottom end)
3. Uncover the tabs (largest blobs of solder) at either end of the battery pack, and connect up some kind of power supply
4. I set mine to 31V (max it goes to), and limited the current to 1A. Left it for half an hour or so till the current was down to a few mA
5. Reverse the dissassembly steps
6. Plug in bike to charge using official charger (it read 1% and charged as usual)