On 2021-06-04, Paul wrote:
One weakness of lithium, is if you let it run down,
below the "low" fill line, the charger will refuse to
charge it. For safety reasons (plated out lithium).
I expect the reason the mower was unusable after
four years, is improper maintenance over the
winter interval.

I've had a battery mower - this is it's fifth season. Removable batteries.

Curious what you consider "improper maintenance" - not recharging
batteries? I always keep mine charged. But what else is to do over
winter on an electric mower? I always clean mine out every other cut.
I suppose re-sharpen the blade.

Jim