One point I forgot to emphasise.

Good insulation is REALLY important - I used it on the negative battery connection (blue wire) as that was the easiest place to ensure the two terminals remained isolated.

On the old NiCad stack, I deliberately shorted out the connections to see how hot they would get (remember this was an old battery that hadn't been charged for six months).
The 1/4 inch metal connection tabs glowed ORANGE ! I have no doubt that if the battery was fully charged it could easily have caused a fire.

I dumped the batteries in a bucket of water and left them outside overnight; there was too much gas from electrolysis for me to feel comfortable about leaving them
in the garage, before taking them to the battery disposal facility at our local tip.

So please take care with your insulation if you perform this replacement; these battery packs have a lot of oomph behind them.