For that new NiMh pack you really need to charge it at a low rate, say C/10 or about one amp or less for a day or two. Half an amp is even better.If the cells are any good they do self balance and then you can charge it with the regular charger. Otherwise, as state by others they will probably be reversed at the end of the miles you travel and damaged.
E-bike stable at our house
Bike-e electric front brushed C/L
Steintrike Mad Max full suspension trike rear 9C
Sun USX delta trike 9C front wheel sort of front suspension
Frame of homebuilt trike in shed with Bafang still on it
New Agniusm/A123 on the Steini and old 10ah Ping paralleled with 12 ah Fatpacks on USX
My wife and I ride the trikes