I had this flashlight from Einhell lying around, which came with a hand drill and 2 battery packs, but the light that came out of it was meh at best, so I decided to upgrade it.
The necessary parts were bought from FastTech, which was actually my first order from them, very happy with their service; but I digress.
Image taken from (site is in German):
https://www.conrad.de/de/akku-bohrschrauber-set-rt-cd-108-li-kit-579519.html
The battery pack has 3 Li-ion 18650 cells connected in series, for a total of 10.8 volts, that’s why I went with a 12V driver.
There was a lot of space left inside, so the everything fits perfectly.
Took me about 2 hours to put this thing together.
With the new reflector it has a lot more throw, compared to being completely floody originally.
The new parts cost me $4.58, so I believe this was a really good investment.