the cables are soldered on to a flat base flush with the top of the Battery.Hi Pete
They are almost certainly a standard size as made by Yuasa, which is quoted as 151mm x 98mm x 97.5mm L x W x H. The extra height is due to the fact that Yuasa include the height of the spade terminals, so the body height is almost certainly 95mm.
Can you confirm that yours have quarter-inch spade terminals? If so the Yuasa part number you require would be NPH12-12. The alternative - NP12-12 - is not really suitable as its capacity is much reduced at the sort of current an e-bike demands when compared to the NPH version.
This size is also made by other manufacturers, but Yuasa is the best known make. They also manufacture under the name 'Enersys' in the States.
If you're in the UK, Maplin stock the right size - their code is UD03D, and they're priced at £32.99 each. Their life will vary depending on whether or not they match the NPH or the NP versions - there's no way to know. I don't think they're made by Yuasa. It would be a start, though.
Edit: just seen John's quote. This might be a better bet as they will be high-discharge models, and a slightly better price, although carriage will be considerable.
Rog.
the question is do I want to risk an other £100 on what my be just the start. of other costs