USB usually provides 5V (or even more, for example 9V with Qualcomm Quickcharge) and the phones contain a single li-ion cell with 3.5-4.3V, so there must be some dc-dc converter in between.
I wonder if it is typically a switching regulator and what efficency they provide in the smartphone environment? After all, how much energy input is needed for a given nominal battery capacity?
I could not find concrete numbers on this, the more detailed power bank calculations only go to the 5V output and then assume the same current at the phone battery, like a simple linear regulator. Which seems to be pretty close in practice? Has nobody done any real mesurments so far?
Hints to battery managment IC datasheets from common smartphones are also appreciated.