2 cell 7.4v battery with DC jack connector can be charged with this charger. 

Polymer Lithium Ion Battery (LiPo) LiIon CHARGER  2 CELL 8.4V 0.5A 2.1mm female DC PLUG -mBot ranger, Ultimate robot or any decide with 2.1mm power plug

Charging unit for the 2 cell LiIon batteries of 8.4V and charging rate 0.5A.

The charger connector is 2.1mm female DC Plug

This charger is ideal for the LiIon battery - 7.4V

Ideally for this battery -