Posted this at blackmagic as well : I have stumbled upon this: https://muxtronics.nl/powerbank.html if only I could contact the person. Maybe if he receives 50-100 demands, he would take it in production. This powerbank seems like the ideal companion to the p4K : constant voltage, programmable (!), variants with more 18650 cells are possible. The standard form factor is really small, and fits the smallrig powerbank holder perfectly. I want to order one, have tried contacting,