A battery's "Ah" refers to the amount of charge it can store. It means that a battery with a higher Ah also has more power. The Greenworks 60V battery has a capacity of 4 Ah and is quite powerful. This model does not have advanced safety features. Provided it is used as directed, and due caution is exercised, it is a safe lawnmower to use. The charger has a feature that will activate the built-in fan if the battery becomes too hot during charging. This will prolong the life of the battery but will slow charging down slightly.