Simple, my local supplier said they did not or could not get this type of battery anymore, you could supply one off Ebay. The last one was19 years old, it still held a charge. I'm going on a car rally, so replaced it in the full car service! Old one now in another car still working!
Wanted a new battery for '76 Morgan. This is the only one made these days which fits but it arrived quickly at a good price and is exactly as described. Only snag the carriers had obviously ignored the "keep upright" bit and the inner plastic bag was damp with a bit of battery acid which had come out! No effect on the performance and the Morgan didn't mind!
Good job!