@eric - Most of those power banks shut off their output when connected to a charger, so they are useless as UPS-type devices. The industry is moving away from the older units that did pass-through power, because they overheat and also tax the limits of the incoming power to both drive a device and charge the battery at the same time. I have a growing collection of off-brand units that people claimed did pass-through power, and at this point could have saved money by just getting a desktop computer UPS in the first place.
As I side note (here we go again!), I just saw this on Amazon and it was tempting enough where I just clicked to order one:
Obviously only useful to those of us in North America with our wimpy 120 volt mains/wall power, with a footnote that some of the reviews hint that these may be old stock with stale batteries. (My weather shelf has two Raspberry Pi computers, a Davis Envoy, and the WF Hub…so this unit is almost purpose-built for my particular application.)
@luukveltkamp - Both the Air/Sky and Hub are supposed to buffer data during times of communications problems. If the Hub loses power, the Air/Sky will send their buffered data when power is restored to the Hub. If the Internet link drops, the Hub will store data until the link comes back up. There’s a post here detailing the buffer size, and I know that I have seen reports of it taking an hour or more for the data to back-fill on the WF site when a Hub is catching up following an Internet outage…