DIY Rechargeable Battery for Headlamp Petzl MYO RXP (similar to Petzl CORE, Just Bigger AA Size)

I had my old Petzl MYO RXP Headlamp kicking around, not seeing much use lately as I upgraded to a rechargeable model. It recently fell into my hands and I thought I could probably make a rechargeable battery for it fairly easily and much cheaper than the Petzl Core which would not fit in that particular models AA (LR06) battery bay anyway.

For materials I used the following:

3x 14500 li-ion cells (I bought some with metal stripes already spot welded, as it is not recommended to solder directly to the cell's terminals)

1x usb-c 1s li-ion charger (mine is based on the TP4056 chip)

2x short wires

the total cost is about ~15$

Now just connect all the cells in parallel and solder them together.

+++ It is important to connect the cells in parallel as the voltage of a singe lithium-ion cell (4.2V when fully charged) corresponds roughly to the voltage of the original three AA batteries in series (4.5V when fully charged) ! +++

Next solder the positive and negative battery connections of the to the respective side of the battery pack. I didn't include under voltage protection as the Petzl MYO RXP cuts out below 2.5V input voltage which is still a safe operating range for the lithium-ion cells.

Make sure to check for correct polarity when inserting the pack! On the Petzl MYO RXP the negative (-) has to go towards the cable that connects the battery compartment with the LED unit.

This is not a officially recommended upgrade, I will take no responsibility for any damages in case you decide to recreate this project.

I will eventually add hot glue, to stick the cells together more sturdily and waterproof the board with epoxy. You could probably desolder the USB-C connector and extend it off the board to make the pack fit more neatly in the battery bay... Right now it sticks out a little, but the silicone back cover of the MYO allows for some extra space.