Originally Posted by Reegor
I have a Hitec radio system, and I still use external BECs as well as using the direct-to-battery power for the RX. Admittedly, this is overkill since the RX power is good down to about 4? volts. That is, a 3S battery would have to be way beyond dead and the RX would keep going. The RX is powered off the main battery, in parallel with the ESC power. This also gives automatic real-time telemetry of the main battery voltage, which allows longer flight times.
Given how well the Hitec system has been working, I am now putting BECs only on my larger planes where I expect lots of servo load.
On this plane the problem is that the internal BEC is not sufficient to power 6 servos (even though it is not often that all 6 are being used). Several folks (including myself) have reported how hot the stock ESC becomes after a short flight. That is why some of us use an external BEC that is designed to handle the servo load. It does not have much to do with the capacity or lack thereof by the LiPo. FWIW - Following that logic, I always use an external BEC on ALL my planes with 6 or more servos.