The battery is the same as the rest of the bike in that it's made in China.
Should the 'maker' go out of business, you might be able to track down a battery to fit.
BMS Battery - in China - is the starting point.
They have a couple of batteries which might be the same as the one on the Mate bike.
Another option is re-celling the battery - refilling the existing case with new cells.
Nearly all ebike batteries are made up of banks of rechargeable AA cells wired in series and parallel to give the desired voltage and capacity.
Cost comes into it on a cheaper ebike.
A new battery or a re-cell will be a few hundred quid.
Some supplied batteries last several years, by which time many owners will think they may as well replace the whole bike.
History suggests a new battery will be available for your new Wisper, the company has been around for years and David who owns it is very keen on keeping spare batteries for all Wisper bikes.
https://bmsbattery.com/70-36v-li-ion?p=3
https://bmsbattery.com/ebike-batter...ty-18650-battery-cell-ncr18650pf-battery.html