Portable power bank for in camera battery charging: Recommendations?

[ellisson]

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I'd like to have in-the-field battery charging capability for my Q3 using a power bank that I can easily slip into a small camera case.  I see that Leica recommends using a power source with output of at least 27W, and 9V at 3A.  Most of the slim portable ones such as the nitecore NB10,000 gen 2 quick charge USB/USB-C do not quite meet these specifications, for example, 38 W, 9V/2.2A.  I wonder what other Q owners are using for power bank charging of the camera battery.   Recommendations and suggestions for a small portable charger would be much appreciated!