Why do you cycle the battery? Do you do this every day ? If the unit was constantly on I could understand why something like this might happen . Some batteries only have a life of a few hundred charges.
"Cycling a multicell battery into deep discharge to overcome a memory effect can cause cell reversal and do more harm than good." [Link: en.wikipedia.org]

I just put it in the charger when it is low. Usually overnight once every ten days for the 9400.