Ok, thank you for your advice. These are the 3 I’m considering. Tempted by the big triangle one for range, I know it would be considerably heavier.
https://electroncycles.co.uk/product/arriving-in-7-days-52v-15ah-shark-downtube-electric-bike-battery-samsung-30q/
https://electroncycles.co.uk/product/52v-20ah-60a-triangle-waterproof-tough-abs-battery-with-3a-charger/
https://ebikebatteries.co.uk/product/52v-17-5ah-panasonic-ncr18650ga-tiger-shark/
https://electroncycles.co.uk/product/arriving-in-7-days-52v-15ah-shark-downtube-electric-bike-battery-samsung-30q/
https://electroncycles.co.uk/product/52v-20ah-60a-triangle-waterproof-tough-abs-battery-with-3a-charger/
https://ebikebatteries.co.uk/product/52v-17-5ah-panasonic-ncr18650ga-tiger-shark/