NIMH fast charge rate???
A C/10 charge rate is 10% of the rated capacity during an hour. For your 1650 pack, that would be the 165mah charge rate, for 12 to 14 hours.
Its usually safe to fast charge NiMh packs at 1C rates, which would be the actual rated capacity in one hour. For your 1650mah packs, that would be the 1.65amp rate. However, this should only be done on chargers that are designed to charge NiMh packs at that rate. You can't use a NiCd charger. If you are using a NiMh charger, you can also treat your batteries a bit gentler by using a 3 or 5 hour charge rate. That would be approximately 650mah for 3 hours, or 390mah for 5 hours.