One thing I do also have is a portable power pack. Handy (if you do have access to 12v or mains for charging). Though you can get some power from them before discharge. If you get the right connections, they very good as a back up. My one (50,000 Mah), even has a LED torch built in!
I have just spent about half-an-hour typing all the tests and justifications, explanations and attaching a series of photos for it to say 'too large' and then its disappeared.
So here is a very brief version :
Is yours the 'solar charging' version ?
Basically your 50,000Mah power bank is probably 4Ah.
50,000Mah is the same as saying 50Ah, A typical car battery is 50-80Ah.
there is no way that these little power packs are 50Ah.
I have done a lot of tests with mine and it is actually 4Ah.
You can test your own. Take a known load and see how long it runs from a fully charged power-pack.
Mine did 14 hours 5 minutes running a 300Mw load, which equals 4.2Ah