Winter storage

[bertsmobile1]

The OP never mentioned just what mower and the type of battery pack in use.

Li-on packs should be kept at 40-50% charge when in storage over 3 months. They should NEVER be left fully discharged or charged and never kept attached to a charger! There are plenty of articles on all of this!

Depends upon the exact chemistry and there are a lot of different ones
The important thing is the battery & charger needs to be in a spot that will not catch fire & burn your house down should the battery fail & blow up
Hopefully large Li batteries will very shortly become a thing of the past as insurance for EV-s is becoming astronomical
Note Testa is now going to Li-Mn battery which is supposed to be immune to thermal run away
Toyota is currently rolling out a solid state Li battery & is also looking at Al-air battery
These are also Li-Mn-Ni batteries that do not suffer thermal run away and cost 1/3 of the same capacity Tesla Battery although Tesla is also looking at a very similar chemistry solid state battery ( because Musk refuses to pay any other company royalties )