Run Fairy Lights on Rechargeable Battery

I am hating single use batteries, so I decided to run these fairy lights for my girlfriend from an old (or a new one) li-ion cell from a notebook. For charging and protection I am using a TP4056 with integrated protection circuit. Connection Type is USB-C.

At first I have to remove components like battery springs and switch which will be used later again. The housing for the two AA batteries is too small for my new 18650 cell so I have to use an other enclosure. I desoldered all wires from switch and springs.

In the second step, after desoldering the wires from the switch I connected these to my lab bench power supply. I set three volts, like two AA batteries. The current @ 3V is about 94mA. With this conditions I calculate res. let the app Electrodoc calculate the values for the resistor.
The given values result an resistance of 12,7 Ohms. Sadly there was no value that was close enough to my result, so I had to connect two 33R resistors in parallel to get an value of 16,5 Ohms which is suitable for me. With this resistance I recalculated the forward current of my leds to ensure, the were not to dark.

As a last step I had to cut out the required holes in the 2x 18650 storage box which can be found cheaply on eBay, Amazon etc. I made a cutout for the switch, the led wires and the usb c plug. I used a normal carpet knife for this. I glued everything, including the battery springs with hot glue in space. For the charger this was not my best idea, because it's getting quite warm but everything keeps in place. The schematic is pretty easy, the battery is connected to the charger. On the protected output the negative wire from the led is connected directly and the positive wire goes first to the resistor and then to the switch. I made a knot on the led wires to ensure there is no force on my soldering joints inside.

With this simple steps you could run everything with leds and batteries very easy from an old laptop cell. Costs are less than 1€ for additional material.