I have JR R700, Futaba AFS, and hitec RCD 3500 recievers. Will the JR 4N-600 4.8v 600mah RX battery work with the futaba and hitec recievers? or do I need match brand of RX with brand of battery? I know Hitec and futaba are compatible, but can I throw JR in the mix?

no rx knows the differce, As long you supply the proper voltage all will work

are the battery connecters the same? will they plug in to the RX?

As long as you connect positive to positive, negative to negative it will work. I believe the connectors will fit, but if using a Futaba connector you may have to trim the little tab off to plug into other makes.
Dennis-