RE: Battery Pack for RS300
You can use either a standard universal (JR) connector or a JST (BEC) connector. Here are just a few options:
DYN1410 5 CELL 600AE MAH RX NICAD FLAT
DYN1411 5 CELL 600AE MAH RX NICAD HUMP
DYN1412 5 CELL 600AE MAH RX NICAD: GTX
DYN1415 5 CELL 1000MAH NIMH RX FLAT
DYN1416 5 CELL 1000MAH NIMH RX HUMP
DYN1417 5 CELL 1000MAH NIMH RX GTX