I have a power bank with a broken USB connector, but a working battery charging module.
It uses a 26650 lithium battery 4000mAh 3.7V .
I figured out how to use a lithium battery for a light saber, but, I had to solve two problems.
It is necessary to coordinate the supply voltage from the lithium battery 3.7 V for the diode in the saber.
The old battery compartment has 4 batteries each 1.5V, 6V in total.
The power bank outputs 5 V to the USB through the charging module or 3.7 V from the contacts on the battery. I ordered a boost module from Aliexpress for $2 from 3.7 volts to 6 volts and connected it in parallel with the USB charge module to the battery contacts.
https://aliexpress.ru/item/32902451567.htmlIn total I have 6 volts output, like a battery assembly on old batteries.
Now I need to install the lithium battery with power modules in the saber handle.
My friend printed out an adapter for me on a 3D printer.
The outer diameter of the adapter is equal to the inner diameter in the saber handle, and the inner diameter is the same as the size of the accumulator.
The new battery fit snugly into the saber without gaps.
It works!
A few photos.