Been seeing quads designed with built-in 18650 battery bays (e.g. RekonFPV). On one hand, they are very convenient for switching out batteries. On the other hand, I worry that the battery bay contacts are not suitable for high current applications (max 30A of VTC6). Can they replace the soldering of a proper battery pack?

TL;DR the holder adds 2.63 mOhm for each cell connected in series. At hovering throttle, a micro-quad powered by 4S 18650s will experience +0.1V voltage drop and +1W power consumption. Not ideal, but somewhat acceptable I guess...


To find out, I bought some 18650 holders off AliExpress. They come in sizes of 1S,2S, and 4S (and they look exactly like the one being used in Rekon35). The 2S version weighs 14.6g. They will break in crash, I have already broken a few.



I am using the YR1035+ battery internal resistance tester. The VTC6 cell is tested 12.86mOhm standalone, 

Versus 15.49mOhm in the battery bay. In other words, the contacts add 2.63mOhm for each cell in series. 


To put that value into perspective, I tested a 3cm piece of AWG 14 wire, which measured <0.01mOhm. 

Cutting the wire into two pieces and soldering them back together (deliberately offset the wires a a little so that current has to go through the solder joint), and resistance measures 0.24mOhm. 

Since soldering has to be done on both battery terminals (~0.48mOhm total), the battery bay contacts are ~5.5 times the resistance of soldering. 

Consider a 4S micro-quad powered by 18650s, it typically requires 35% throttle for hovering (~10A). That means at hovering, the contacts alone are causing ~0.1V (10A*2.63mOhm*4) voltage drop at terminals, and 1W power consumption. Not ideal, but somewhat acceptable I guess.

Conclusion: This stuff is being sold at $0.7 a piece, I think I deserve the Cheapest Product Review of the Year Award.