Given the number of complaints from MobileRead users about weight, suggesting adding a battery pack that would markedly increase the weight is not likely to be popular. Oddly, the unit being sold on Amazon claims a weight of 90.7 grams while the average weight for a 10,000mAH lithium ion battery in the samples I checked on Amazon.ca varied from 150-200 grams. One example is
https://www.amazon.com/dp/B0GDTPFQ3P weighing in at 171 grams. Add the case, etc. and it's likely to weigh more than my Libra Colour.
To make it more fun, I checked the specs on 4 10,000mAH power banks with wireless charging. The lightest clocked it at 200 grams, the heaviest at 249 grams.
Personally, I feel for Kobo's ereaders, a power bank and cable would be a cheaper solution. One friend of mine did add a wireless charging receiver to his Clara BW (GOWENIC, about 15 grams) but then he needed the sender and a wall wart to power the sender though it also worked with an Anker power bank's wireless charging. The same one that my iPhone shows slow charging when I tried using it.