I agree you could charge the battery from a source that cannot provide as much current as desired but the voltage level has to be high enough so they are doing some magic with USB or the battery pack to charge a 7.2 volt pack starting from a 5 volt USB source.
But the problem is the emphasis is on "smart charging" technology now which means different things to different companies. The bottom line is it is more complex and the charging circuit itself is very particular about its own power source in terms of voltage AND current capability so it may not function at all with an insufficient source.
This is common across product classes. For example, modern vehicles have a pretty amazing array of driver assist features providing enhanced stability and traction control during inclement weather or during emergency or ill-considered maneuvers. But these systems depend upon the engine and transmission responding instantly and exactly as commanded by the assist system routines and if there are even minor issues with the powertrain then these safety assist systems are instantly disabled. It makes sense that they depend upon the powertrain responding exactly as commanded BUT it means the safety assist features may not be available at the time they are most needed. This is one of the issues of increasingly complex systems which create additional failure modes, often arising from difficult to foresee higher order interaction effects. I spent a lot of years doing quality and risk consulting and adding product complexity, often through feature creep, exponentially increases the problem of maintaining quality and a low rate of aberrant behavior and/or outright failure.
And on edit: a new browser on my laptop grabbed older password files from my former browser so this was posted using my original Canon forum credentials.
Rodger
