It doesn't need to be lithium. Nickel-Iron batteries are very good for this purpose: practically unlimited charge-discharge cycles and overcharging/overdischar

It doesn't need to be lithium. Nickel-Iron batteries are very good for this purpose: practically unlimited charge-discharge cycles and overcharging/overdischarging won't damage them. They should be dirt-cheap too, but almost there are very few manufacturers so there's not much competition. https://en.wikipedia.org/wiki/Nickel%E2%80%93iron_battery https://en.wikipedia.org/wiki/Nickel%E2%80%93iron_battery