If the battery will be dedicated to the ua5, just cut your cable in the center and swap the wires, solder them together and heat shrink over them. Otherwise, have ted make you a dedicated ua5 cable so that your stock battery cable can still be used for normal polarity applications.
Reverse polarity devices can be a pita for this reason.
Impotant tip...label this cable as reverse polarity so you dont accidently forget a year from now and burn another piece of gear. Most gear has reverse polarirty protection, as your us5 does, but not all gear has it.