The whole idea is not to discharge battery too much and keep it at high charge level as much as possible, which in reality means charging it every night. Doing so could probably extend it's life past 4 years. I have Sony video camera Li batteries that lasted at least 5 years but they weren't used too frequently and at some point failed to the point they won't take charge no more. I speculated that battery self discharged over period of almost one year of no usage bellow minimum voltage and now the charger won't allow it to be recharged.