Save your expensive toys with miniature automatic power guard. Based on Schottky diode device choose higher voltage itself from two independent power sources. Device equipped with micro switch to activate backup battery so you do not need plug/unplug cable every single flight. Comes in three backup battery plug versions: with stardard servo connector, with red JST SYP connecor or JST PH 2.0 for 1S LiPo (or LiHV). Wires lenght is 80 mm for power sources and 100 for Rx but you can order any of them as custom so device and its battery can be installed in different locations depending on CG, space availability, etc. without use any extensions.
Prices:
1. Standard 10A, input 80mm, output 100mm, 26AWG wires, with micro switch - $15
2. Custom 10A, with shorter wires - $17
3. Custom 10A, with longer wires  - $17+ (depends)
3. Standard 30A, input 80mm, output 100mm (or shorter), 22AWG, no on/off micro switch - $21
4. Custom 30A, with longer wires, no on/off micro switch - $21+ (depends)
The shipping cost is same for up to 10 devices shipped in single packet so order more than one and save) 
Technical data:Size - 28x10x8mmWeight - 7g (with 100mm wires)V,max - 30Direc voltage drop - 0.17V measuredVoltage switching difference, min - 0.5V