Regarding 8.4V Ni-mh Batteries and Smart Chargers?

I am currently using a 1100 mAh 8.4V Ni-mh Battery for my airsoft gun (JG G36C). I understand that using a 1500 mAh or 3300 mAh battery that was still 8.4V would last longer, but would there be other consequences, since it recommends to use 1100 mAh 8.4V Ni-mh only? Another question is could someone suggest a suitable, CHEAP, smart charger?