I learned this trick with our mobile FD radios, and its worked ever since on every rechargeable battery I use. Each battery is designed to withstand a certain number of charge cycles before they start to lose power retention. Typically that is a thousand charges or so. A lot of people just leave the battery plugged up all the time, but that will cause them to eventually lose charge. The battery will constantly be charging itself full and then switching off, only to charge it again some more later on that day. Once the battery is charged take it off and use it. Once it goes completely dead, charge it again. If you use it for only 10-15 minutes, dont put it back on the charger. Using it until its completely dead will decrease the number of charge cycles, making them last longer. If you are doing a big job, and have two batteries, put one on the charger when you start using the first one. By the time your first battery is dead, the 2nd should be charged enough to finish the job.