Lego Train 60337 Rechargeable 18650 9v Mod

Intro:

I got tired of replacing AAA batteries in this train.  Also, the voltage of AAA batteries seemed to drop off pretty quickly and the train would start getting slow.  

Overview Video:

BOM:

• 18650 Cell
  • I salvaged mine from a laptop, which was nice because it still had little tabs on it.  I used these tabs to solder my wires.
• TP4056 Charging Module
  • Make sure yours has the battery protection on it. 
  • https://www.amazon.com/dp/B07PKND8KG 
• Boost Converter
  • There are so many of these out there.  Just make sure the one you get is smaller than 40x27mm so it will fit into the printed battery base.
  • MT3608 without port
    • https://a.aliexpress.com/_mLuTqlg 
• Mini Rocker Switch (8.5 x 13.5mm)
  • https://a.aliexpress.com/_mrU1EWO 
• LED Stuff (Optional)
  • 3mm LED
  • Resistor (I used ~400ohm)
• (2) m2 x 10mm screws
• (2) m3 x 12mm Flat Head Cap Screw
  • OR use the alternative versions for Button Heads or Socket Heads
• (2) m3 nuts
• Superglue
• Soldering Iron

Printing:

• Print all parts in the orientation provided.  No supports are needed.
• 0.2mm layer height.

Wiring:

Build Instructions

• 18650 Mount
  • Please see the included wiring diagram.
  • Glue the printed 2x2 brick into the bottom of the 18650 mount
  • Solder 5 wires to the TP4056 module
  • Solder wires to the tabs on your 18650 Cell and route the wire to the side hole of the 18650 mount (where the TP4056 will go).
  • TP4056
    • Insert the TP4056 with its wires into the TP4056 printed part.
    • Attaching battery leads to the TP4056
      • The best way to do this is to have short wires already soldered to the TP4056.  Then carefully cut the wires from the batteries so they meet the short wires on the TP4056.  There is enough space for a small loop of wire for each battery connection.
      • Note: the wires should be soldered so they come out of the front of the board.  Then trim the back of the solder joints close to the back of the board.
    • Glue the TP4056 Mount onto the side of the 18650 mount.
  • Pop the rocker switch into the 18650 mount
  • Assemble LED
    • Solder your desired resistor to the 3mm LED and add wire leads.  I used ~400 ohms.  
    • Using a small screwdriver, push the 3mm LED into the hole on the 18650 mount.  It should pop and then stay in place.
    • Solder the LED- to one of the wires that goes back to the TP4056 (V-)
  • After construction of the 18650 mount is complete, glue the lid onto the 18650 mount.
• Battery Box Base
  • Screw in the Flat Head Cap Screws (FHCS) as seen in the pictures.
  • Attach the output of the boost converter to the back of the FHCS by looping the wire around the screw and attaching with a m3 nut.
  • (+) of the boost converter goes to the taller/middle bolt.
  • (-) goes to the one on the side.