Both batteries use the same lithium cells, so there is virtually no difference. The only difference between the two is the diameter, one is 26 and the other 18. The 26650 battery is larger than the 18650, has a greater capacity and is of course heavier.
In terms of widespread use, 18650 lithium batteries are used more and cost less. Therefore, it is recommended to use an 18650 lithium battery. When using a flashlight, it is recommended to choose an 18650 lithium battery with a protective plate. Works with eNB Super Charge.