So for some reason I had two batteries and two lamps laying around, and I decided to make a working lamp out of it.

No charging circuit yet - comes in version 2.0 :D

The battery:
https://www.amazon.de/-/en/gp/product/B01N7614S0

The lamp:
https://www.amazon.de/-/en/gp/product/B09MW8X5GB

The switch:
https://www.amazon.de/dp/B0D9DDD36J

The fuse:
https://www.amazon.de/dp/B078X977PK

Bolts:
https://www.amazon.de/-/en/gp/product/B0D21TYKQP

It's all M5, on the top in the holes insert a nut, don't tie it till it breaks :)

Some more notes:
I printed it with 15% infill, the housing is ~1mm wider in both directions than the accu, I plan to put there something so it does not rattle inside.
Some basic soldering is needed, from the battery + and -,

• goes for the black wire on the lamp, + goes to the fuse, fuse goes to the switch other terminal of the switch goes to the red of the lamp - c'mon you know this.

For fues I recommend a 3A type - as long as it is smaller than the short circuit current of the accu you will be okay - but why pick a larger than needed one.

Based on my calculations it shall work for 85mins at least, but never tested it. And this is based on the assumption that 42W is 42W with 12V and so - I doubt that this thing eats 3,5A - and the 3A fues did not get blown - maybe I missing something, maybe it is just not 42W :)

As always: You are absolutely free to download, print, modify, sell whatsoever makes you happy, the only thing I take no responsibility for anything you do.