For anyone who’s confused as to how this sorcery could work, it’s due to the chemistry/physics of the battery. As batteries discharge, there is more crystal growth of the electrolyte. Crystals can store mechanical energy like a spring, while the electrolyte in solution absorbs energy. It’s like dropping a water balloon vs dropping a solid rubber ball.
This is the lab behind the poop knife. They are absolutely experts in this kind of thing.
I need to read the whole paper, but I suspect the weight/wind resistance ratio of the javelin is better, and that the motion of launching an atlatl dart is affected by the downward angle. The railing on the scissor lift likely has an effect, too.