Building my own 18650 Li-ion 7.4v battery for my 9XR PRO radio … by David HK October 2016

Building my own 18650 Li-ion 7.4v battery for my 9XR PRO radio … by David HK October 2016

***WARNING: li-ion batteries could catch fire, do it at your own risks!

This DIY was inspired by below link:

http://droneinsider.org/upgrade-your-fpv-goggles-to-li-ion/

and the wiring diagram below is also copied from above link.

Before that I was using a Turnigy nano-tech 1500mAH LiFe 3S 9.9v from hobbyking, and it is okay, and last for 2.x weeks of usage.

https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=84472

But since I read the post in the 1^st link above, I have been wanting to build my own Li-ion battery to see how long it will last.

I bought 4x 2900 mAh li-ion 18650 batteries from Taobao, the brand name is called AXLOAD, in yellow, with protective circuit.  I bought this because:

1.  It uses its own brand name, instead of those claimed to be western bands.
2. The stated capacity is in the lower end, normally you see 3400 or even 4000+, and most of the cases are over stated. So hopefully the 2900 is a more true capacity.
3.  It weights 42.8g, and all 4 batteries voltage when I received them are in 3.8x volt, so looks like there is some QC in their manufacturing process.

First I used hot glue to fix the 2 batteries together but 1 of which is upside down as in the diagram above, 

then I soldered a paperclip to join the + & - terminal at one end, 

soldered the charging cable with the red JST connector, soldered the three wires balance charging cables as shown in above diagram, and finally soldered black & red wire with a 3S balance connector which is used by my 9XR PRO radio.

Then I taped the 2 batteries together using duct tape, and for the final touch, wrap the whole thing in a heat shrink tube. Done!