There are, however, USB-PD sources that can run from a fixed voltage DC supply.
I would actually really like something like this that can fit in my backpack with just shy of 100Wh (airline limit) of energy storage, a retractable cable to plug into an outlet, and monitoring via USB. In theory, I could build this myself around OpenUPS, but sourcing a pack, retractable cable and suitable enclosure is really annoying.
It is surprisingly not.
I travel frequently with random ESP32 projects in various stages of looking highly suspicious and never get hassled about them. 4oz of an unfinished bottle of water though is absolutely not getting through security.
Do those have large li-ion batteries? Lets say you'd diy your own charge controller, I could see that get treated differently since you could cause a nasty fire that way.
In London security will sometimes specifically ask if you or anyone else has made repairs or modifications to any electronics. Depending on how honestly you answer, this could still be a hassle.
There are, however, USB-PD sources that can run from a fixed voltage DC supply.
I would actually really like something like this that can fit in my backpack with just shy of 100Wh (airline limit) of energy storage, a retractable cable to plug into an outlet, and monitoring via USB. In theory, I could build this myself around OpenUPS, but sourcing a pack, retractable cable and suitable enclosure is really annoying.