In the past when you use a RX pack, you will either:

1) turn off the esc (but this may disabled some ESC features)

or

2) turn on the esc, but remove the 'red' wire on the esc plug connecting to the receiver. This will basically turn off the internal BEC. Because if you dont, you will fry the BEC circuit.

However, for newer tekin releases (v200 or above) you dont need to remove the 'red' wire anymore.