Hi !!!
what kind of battery ??? Lithium ion, Nickel Cadmium ???
And what kind of use ??? High current burst ???
The lifetime could be increased by lowering the operationnal temperature of the battery. you could decrease the chargind/discharging current, and control carefully the discharge....
Hmm... Let's think a little...
I think a non-constant current doesn't shorten battery life.
In order to improve this you should design a 'constant current source' as a charger.