Anything 'Lithium' has become a buzzword- it's more for extended storage, solar and deep cycle applications and a lawnmower isn't any of those, unless decreased charge level due to sitting is included. Charging is different, the weak electrical systems in mowers doesn't make them compatible and the added cost really doesn't make sense. A good flooded lead/acid battery that's occasionally charged should work for years and if someone doesn't want to charge it constantly, a smart outlet with daily or semi-weekly charging periods will make sure it never goes dead. Even better- install a solar panel of sufficient capacity for a battery as reserve, then run the charger on that or rewire the shop/garage's lights to run on solar and size the system accordingly. Add an occupancy sensor and the light switch won't be needed.