Here's a flash light I made many years ago. I used to buy the rechargeable halogen flashlights, but... they were dead either from not keeping them on the charger or they were dead cause the charging unit failed. In one case the battery got reverse charged.
So I decided to make my own......
I went to one of the auto store supply franchises and bought a set of 12 volt auto fog lamps. This set of fog lams came with a switch and wire harness that also had a 30 amp fuse.
I scrounged up a length of 3/4 inch of PVC pipe at least a 12 inches long. It will need to be cut but more about that later. You can pick up 2 foot long PVC pipes from at least one big box home improvement franchise.
I scrounged up 2 PVC 3/4 inch end caps. As shown in th video I 2 have 2 battery packs which will require 4 end caps if you choose to do the same.
Some tie straps and a piece of flat stock slotted steel.
I'll let the video do the explanation, although when I first made this flash light I only had one battery pack to hold 4 Li-ion 18650 batteries. When I recharge them I charge them at once with four single battery charges I made from T4065 charging boards I got from aliexpress.
The batteries shown in the video I got off of an online auction site and as noted in the video the batteries are marked that they are 6000 mAh which certainly is not true.They are only about 1800 mAh which is fine considering how much I paid for 300 of them. It was about $0.75 each I think, maybe as little as $0.50. I wanted so many for another project I am working on. I have also managed to acquire a number of Li-ion batteries from non-working laptop battery packs which I sometimes use in this flash light as well. I don't mix the laptop Li-ion battery with these "6000 mAh" batteries.
One another thing to note is these batteries even with 2 sets of four in parallel, do not last very long, about 5 to 8 minutes. For me that is all I am looking for. The batteries that are in the store bought rechargeable halogens flashlights usually only last about 15 minutes of use before they need to be recharged and they only have 1 light bulb.
I have been looking at the 12 volt LED lights that are available nowadays and I may switch over to those.....someday.