French researchers have announced a prototype of an 18650 sodium-ion battery ... However, lithium isn’t the only possible choice for rechargeable cells. Lithium has a lot of advantages.

An 18650 potassium-ion battery represents a category of rechargeable batteries that employs potassium ions as the charge ...

So [Travis] decided to upgrade it to make use of the ever-so-common, 18650 lithium-ion battery. Not looking to purchase any components [Travis] performed this hack using simple recycled household ...