This Connector (Series -Harness) is used for joining two like Lipo packs to increase the voltage but maintaining the single pack mAh. Here is an example - If you combine two TP 2100 3SPL packs with this connector you will maintain the mAh 0f 2100mAh but increase the Voltage to 22.2 Volts Use one of to Combine your trex batteries to make a battery for the new trex 500.