Depending on the type of actual battery that is in them there are some things you can do to extend the life of them. I am looking into what specific type it it. I suspect that they are Ni-cad. Ni-cad batteries do not like to be left in chargers. They do not like to be only partially discharged and then recharged. You should use them till the are almost dead. Then you should charge them up fully and remove them from the charger. If you keep letting it only partially discharge it will develop a memory and when it hit the memory spot it will just suddenly go dead. Other things that improve their life is keeping them cool. Quick charges will use them up quicker than a slow charge.
Lithium Ion and Ni-mh batteries are not as picky as a Ni-cad.
Also keep the contacts clean and free from contaminants. They can cause a short over time or a bad connection.
I know this because was a Ham Radio operator and and Electronics tech. If you are a Ham you become a Battery Guru or you spend a lot more on batteries which can get old.
Hope this helps.
FYI all Ecig users should become battery savvy. It will save you money.
I'm careful with how I charge my laptop, since the battery is difficult to replace. I never thought about taking the same care with this battery. I am rotating between batteries, do that will help. I will make sure to drain them down before recharging. thank you for the reminder