I was very careful to apply a vacuum cleaner nozzle while cutting. I also cleaned
up the cut edges and taped over the 'door' when closed.
Keyboard easily replaced and job done.
So you can do that simply by removing the keyboard and nothing else!
Again, thanks Malcysblog for the detailed information. I couldn't have done it otherwise!
Oh and I must add that the laptop's up and running as I type.
(PS, I found very similar volts drop - old battery 3.1 and new battery 3.5 volts.)