This battery adapter cable allows you to plug two batteries with EC5 connectors together in series to power a single speed controller. This cable is built with 12 AWG wire to be able to handle the higher currents of larger aircraft, and has an overall length of 12 cm (5 inches). To use this cable, both batteries must have the same mah capacity. For example, two 6-cell 4000mah batteries can be connected together to form a 12-cell 4000mah battery. You could also connect a 4-cell 5000mah battery with a 6-cell 5000mah battery to make a 10-cell 5000mah battery.