to be the king of flashlights, but replacing those pesky D-cell batteries is kind of ridiculous in this day and age. So [Travis] decided to upgrade it to make use of the ever-so-common ...

If you do not want to purchase from the links below, please ensure that the battery meets the above requirements. Amazon bans the sale of 18650 batteries, but you may still be able to find some there.

He’s working on adding a huge number of 18650 Lithium cells to his home ... brief about the Powerwall (Tesla’s whole-home battery storage system) and was like, “hey, I can do that.” ...