NITECORE NB10000 Ultra-Slim 10000mAh QC Quick-Charge Power Bank with USB and USB-C Dual Outputs and Cables for Phones Flashlights and Headlamps https://www.amazon.com/dp/B08JH5SKQ8/
You say the NB10000 costs $100 several times. The NB10000 is $55-60.
I place this Anker battery in a central pocket. I recently bought a Nitecore battery for backpacking that I’m confident would fit too.
Anker PowerCore 10000 PD Redux https://www.amazon.com/dp/B07PXMF52C
NITECORE NB10000 https://www.amazon.com/dp/B08JH5SKQ8
Ive seen this one recommended on other subs