This is an adapter charge lead for the battery that comes with the mCP X, the EFLB2001S25. This mCP X battery comes with a new, larger connector than the other UMX batteries and this adapter is used to adapt the larger connector to the current UMX connector, which allows the battery to be charged with the current UMX chargers.
This is the E-Flite 500mAh 1S 3.7V 25C LiPo Battery with the High Current UMX Connector. This is the replacement battery for aircraft such as the Blade Glimpse FPV.