Power Bank as main power source?

[Pumping Iron]

I may be on the wrong track here, having limited knowledge of the subject, but would it be possible to use a high capacity "power bank" as a substitute for the stock battery pack in a detector?
I am thinking particularly of the Whites "tdi sl", which has a short battery duration.
The latest power banks are small and would seem to hold a massive battery life, with several at 12v and above.
They seem small enough to fit in the battery pack compartments of some detectors.
Feel free to rubbish this idea, on condition that you explain why this is a non starter?
Rough example ----
https://www.amazon.co.uk/8000mAh-Coloured-Portable-Starter-Laptops-Blue/dp/B01J6DSNU0/ref=sr_1_4?s=electronics&ie=UTF8&qid=1510947366&sr=1-4&keywords=12v+power+bank

 

[LE.JAG]

Yes you can
provided you have a constant output voltage
at the right setting for your detector
for the 13.5 volts sl would be a good thing
a perceptible gain on the acquisition limit targets
valid for all IPs

I'm not sure that the battery of the example comes out 12 v continuously ?

Personally I use a homemad pack for all my detectors = the blue box
a lipo of 22 v with a regulation card following the machine
18v, 16v, 13.5v ......
just a connector to add and I wear it in the back
in a hunting jacket, very practical