Any Ni-MH battery not specifically designed for high discharge/charge should not be fast charged if you want many cycles.
Basically any size other than Sub C batteries for buggies fall into this category.
The best charge for a high cap. Ni-mh is a 1/10 C for 12 -14 hours.
So john S's suggestion of a spare set makes sense.
A suggestion for a charger, get a 4 button smart charger, there are many brands but all of them can charge nearly any battery you can throw at it and with the correct type of charge for that battery.