Hi
No, there's no need to totally discharge the batteries, it's quite safe to charge it from partially discharged since Li Ion batteries don't have memory. The charger is intelligent and will cut out when the battery is fully charged.
If you've got more than one battery try to cycle them though so one isn't staying unused for months at a time.
We're going to produce an info sheet on battery care, I'll post up when it's done.
Hope that helps.
my orders are to sit here and watch the world go by