They can be re-charged best with smart Ni-MH battery chargers
These are manufactured in the USA by Batteries America
RLI-007-1 : 3
6-volt battery packs provide better operating voltage for larger servos
5HRAULAF : 6.0 volt 2150mAh NiMH battery for Futaba. Replaces HT5F1800B, HT5F1700B SAT battery They can be re-charged best5HRAULAF: 6 volt 2150mAh rechargeable high capacity battery for Futaba RC transmitters. Replaces original battery # HT5F1700B , HT5F1800B. Provides more operating time than original battery. Fits Futaba transmitters such as T10J, T4PK, T8J, T10JA, T6J, 4PX, 4PL, 4PKS, T14, T14SG, 14SG, 4PK FASST, T12K, T12, 12K T FHSS, 16SZ etc. Re charges thru the radio (if equipped with a charge jack) with the original stock Futaba wall charger, or with an external