STIHL batteries can be charged with either the AL 300 quick charger or the AL 500 high speed charger. Each charger features a different charging capacity (Watt). If you are using Cordless tools for long periods of time it's a good idea to have two batteries to avoid down time.
A comparison of battery charging times
The batteries can be charged several hundred times without any appreciable loss of energy. Here you can see an overview of the required charging times of the various batteries.