[engolling]

Since there will be a view pieces of the first version in the field soon a brief summary from my side:

The system will output the same voltage as you have on the input side minus the foreward voltage of the used diode. That's why I recommend a oversized Schottky diode.
Be aware that you will have to adjust the DC/DC converter after the battery to a voltage slightly below the voltage at the output, otherwise there will be a steady current over the charging borad.

I also recommend to solder the boards directly to the connection board with 1mm wires or similar and put a spacer below. Pin headers also work but lead to instability and voltage losses due to bad contact resistance.

The following parts can be used:
 

• SBX 3030 Schottky diode or similar
  
• TP 5100 Lithium-Ion Battery Charger board
  
• FDC 2s-2 protection board alternative a HX-2S-JH20 board will fit
  
• 2s 18650 cell holder THT version with pins
  
• 2 18650 Lithium-ion cells (not LiFePo)
  
• NC bimetall disc switch 45°C
  
• XL 6009 DCDC converter (with voltmeter and without voltmeter)
  
• fuse holder 5x20mm for THT mounting
  

If you have questions if a specific device will fit, don't hesitate to write me.