So, my advertisement smorgasbord delivered this gem
https://www.ebay.com/i/124274846648?itemid=124274846648&norover=1&siteid=0&mkevt=1&mkrid=711-198453-24755-9&mkcid=16&ct=71&tag4=23846282153720478&tracking=23846282156780478&fbclid=IwAR12g_xSQtHBm9X-qmx-iPrANhvBeRajWfzGJn7nSji8yncE3lPhQib9-HU

2,000,000mAh USB battery
At 5 volts, that works out to about 10Kwh in Size: Approx.
16x7.5x1.5cm about 0.000612 kl
About 16Mwh per kiloliter!.

Yeah BABY!
Time to design me some new TL10 dinghy's....
..
(/sarcasm)
That's some pretty deep power density, isn't it?