I was cleaning out some old stuff in Alex's closet and came across an instruction sheet that came with our lithium ion batteries.
I'm copying some of the wording I found on it. I hope it's helpful to some for improving the life of your batteries. I can't imagine having to go back to using those big bulky heavy batteries again.
Expected Cycle Life
A cycle is the degree to which the battery is discharged before being recharged. The cycle life (number of cycles) of the battery is determined by the depth of discharge the battery continually encounters. The less a battery is discharged before being recharged, the longer the cycle life will be.
The battery is a Lithium Ion type battery; therefore, it has none of the memory effects seen in rechargeable Ni-Cd batteries ("memory effect" refers to the phenomenon where the apparent discharge capacity of a battery is reduced when it is repetitively discharged incompletely and then recharged) and does not have to be completely discharged prior to recharging.
Hope this helps.