We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember Lobster
saying something like:

Does the Ah rating matter as regards my charger; is it simply that the
higher the rating the longer it will take to charge and the longer the
charge will last? I've found some convenient/suitable-looking 2.5Ah
cells online - will they be OK with my charger?

Nicads are dropping off the radar and unless you want to change your
charger too, you'll need to keep to that technology.
As an example, www.component-shop.co.uk
Look under Radio Control, Single Cells and see they're all NiMH
nowadays. A replacement charger is cheap enough, though.