I have a 2021 TM 300 EN FI bike, and it comes with this battery:
BATTERIA ALIANT YLP09X 12V EQ. 8AH
You can get these in England pretty cheap:
https://www.roadraceperformanceshrop...attery-12v-8ah
It spins the TM over like crazy.
I am not sure if this had a battery management system built in (basically, a charge regulator), but you could call to find out more.
In the US, this battery costs $250 from TM. If this dies, i'd probably preplace it with a earth x:
https://earthxbatteries.com/shop/etz5g.
This battery is about 1/2 the price of what TM charges.
My $0.02.