I am not sure you are aware of this but the battery charger has to be changed to Male ultra plug as well so that it can plug into the female ultra plug of the battery. See pic.

And when you do the solder make sure the red wire (pos.) is soldered to the vertical plug of the Deans and the black wire (neg.) is soldered to the horizontal plug of the Deans.

Then before you solder the wires to the female Deans plug the female into the Deans male so you can match up the wires correctly. Then when you are sure where the wires go pull the two apart before doing the soldering on the female plug.