NPB4, introduced by NITECORE, is a portable battery that supports 2m water resistance. Of course, there have been many portable batteries that support waterproofing. You have to do the cumbersome work of attaching and detaching multiple times, such as attaching a cover to all USB terminals or removing it from a rubber-like cover.
However, NPB4 supports IP68 even when the terminal is exposed. It has a smartphone-level waterproof ability that is strong against water. Packing is placed between the end of the terminal and the case to improve the sealing around the terminal.
The battery capacity is 20,000 mAh and the output is up to 18W. It can also be secured with something like nylon or the tip of a bag. Related information can be found here.