Hi!
As has been said before. NiMH cells doesn't like to be fast charged in the long run. It can be done but don't expect them to be too long lived.
Then there is the problem with "False Peak detecting" All fast chargers use Delta peak charging and NiMH cells often false peak when you fast charge them. It's therefore wise to slow charge them with 0.1C (in your case 220mAh) now and then and don't rely on the alarm signal the charger puts of when the fast charging stops. The battery pack isn't always fully charged.