Interesting. I’ll get on to them to see if I can get a replacement. I thought it wasn’t right, but wanted clarification first! In theory it should charge 5.7 batteries right?!
20000/3500 = 5.7
No, because the drone batteries are not 5V. See my above answers
For the mini2 the batteries work out at around 17.5w, your powerbank at 50w so you should get almost 3 full charges
For those interested I use a wee app from Red Binary for ohms law, but it also does watts which I’ve just used for the first time. Use it all the time for working out resistance or current draw on motor windings. Completely free and no adds
Dont forget that there will also be losses in the (mini2) charger (maybe 80-90 percent efficient) and added to that the output conversion of the powerbank (70-85% efficient) (converting from the 4.2v of the cell(s) in the powerbank to a 5v output) and also added to all that is the fact that charging a battery always takes more power than it’s capacity (the rest is lost in heat).
Tim
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Thanks @GunjaFPV. I wish I fully understood this because i still don’t even though you’ve explained it very well. Numbers habe bever been my forte.
If someone can work it out for me id be very grateful.
The battery pack i bought is a 20000mAh 20V 65W
An Air2s battery is 3500mAh 11.5v 40.42wh
Does that help and woth those numbers does 1.5 batter charges make sense from the battery pack i bought?
Lastly, if it does add up to be expected thats no good for me, so can someone recommend a bettery pack that will charge 2 batteries quickly, ideally at the same time aswell and isnthat even possible!
If my battery pack appears to be suitable based on the maths then ill get a replacement.
Apologies for being dumb, as much as ive tried i just cant get my head around the numbers. 
You’re not dumb, your numbers to me look correct. The power bank has 65watts, your air2s needs a little over 40watts for a complete charge. Bare in mind that you wont completely drain the battery’s so you might get away with two top-ups if you left around 20% in each battery after flight. If you’re looking for more charges you will need to move to a much bigger power source. I don’t know how big these things get, or how portable you want it to be?
thanks @DazC So essentially ignore all numbers except wattage! That makes life much simpler!
65/45 = 1.4 so the 1.5 batteries is about right!
Thanks everyone for clearing that up, my expectations were way too high because I didn’t understand, but now I do. This is what forums are for! Thanks again.
Oh just to confuse us all as we get to work it out… Watts out, and watts capacity is different! A battery might hold 300W, but it can only supply that at 50W 
So… Volts x capacity is the Watt value you want