Yes it's possible, but it's not something the average person can do for very long.
I can squat 1.5X my own weight, but I still get pretty tired carrying a mere 12kg backpack through a long airport walk. Sure you can build up to carrying 20kg all the time, but it's not normal for most people in the world. And it would not be accepted as reasonable by the people in the world who could afford it.
Soldiers are routinely expected to carry far more than this. They may be carrying it in a more effective pack and/or distributed over more of their body.
Quick google search indicates plenty of US Troops were hauling 90+ pounds of gear around in Iraq and Afghanistan due to need to carry a pack + body armor + weapons.
I'm no soldier but I have certainly hiked with a 50lb load in a good internal frame pack.
And in any case the eBike example was listed. 50lb is not a very heavy load on a bicycle at all. But a battery like this would be better used to make an eBike much lighter. Today they are comically heavy in ways that creates all kinds of extra problems.
If you make the battery 1/4 of the weight of a current eBike with a 100 mile range all of a sudden you don't have to supersize everything on the bike and make it heavy, hard to handle, and un-aerodynamic. It would make the whole bike's performance improve even more.
The key is a good pack like that used for hiking with a proper frame and a large padded belt, not a normal school type backpack that you carry just on your shoulders (often just slung over one shoulder). The proper pack setup loads your muscles more like squatting. The difference is pretty striking. I think 20kg is appropriate in that instance.
(Normal guideline is hike pack should not be more than a third your body weight to avoid injury, which for the average American male would be 60 pounds and the average American female would be 50 pounds… there’s enough margin so that even if you’re talking just those in a healthy BMI of like 23, there’s enough for a 44 pound pack for the average height American male and female.)
