i purchased my 8 x aa transmitter pack from
www.component-shop.co.uk and rang them up to get the best charge rate for the batteries i purchased from them.
i purchased 2 x 3600mah nimh aa packs for my futaba 3vcs and they recommended a charge rate of 500mah (0.5a) to 600mah (0.6a) to conserve battery life.
and as they are a battery manufacturer thats the charge rate i use, so i'd suggest same rate for yours, but its your choice.