This is the Series 10 Gauge Wire Harness from Castle Creations.
Connects two battery packs in series enabling the voltage to be
Series 10 Gauge Wire Harness with two Deans male plugs and one Deans
Connecting to batteries and electronic speed control
Wire Length Between Connectors: 5" (127mm)
Wire Size: 10 gauge
Use only identically prepared packs with this harness. Both packs
must be fully charged and properly balanced. Both packs must be
from the same manufacturer, have the same C rating, capacity and
level of charge at all times. Failure to observe this warning will
result in battery damage.