What is the difference between battery and rated capacity. I tried googling and theres a very technically paper with the definitions...

But what does it mean in terms of using it to charge my phone.

#Aliexpress US $6.15 72%OFF | Essager 10000mAh Power Bank Slim USB 10000 mAh Powerbank Portable External Battery Charger Pack For Xiaomi Mi 3 iPhone PoverBank
https://a.aliexpress.com/_sZXhqk

To me this looks like a marketing lie. Either its 10K or not. I would avoid.

Get some name brand powerbank. Like www.anker.com or www.ravpower.com
Costs a bit more but you'll be probably happier with it long term.

@WildOrangutan I would think the same but 5/3.7 < 10000/6500. Or that would mean that they take the losses into account with the 6500 figure.

Shady Chinese grey factory runs are shady. Buy a name brand.

Li-ion cells have a nominal voltage (when fully charged) of 4.20V and (when nearly fully discharged) of 3.7V. Battery capacity tells you how much mAh you will get from those cells but only at their nominal voltage. Rated capacity is lower because it actualy tells you how much mAh the powerbank can provide at 5V (standard charging voltage at USB standards) it might or might not include losses. Why rated cap is lower? Energy conservation.
E=Voltage[V]*Charge[mAh]
So if you want more voltage you will get less charge.

People might tell you that you should only look at rated capacity cuz it is smaller and it is what your phone will get but remember that the phone takes that 5V and lowers it to its Li-ion cell voltage so it actualy gets a bit more charge out of it.

To sum up
Cell capacity: capacity of the cells inside the powerbank at ~4-3V
Rated capacity: capacity of the powerbank at 5V output

@heyheni $40 that's a pretty steep difference for quality?

Would need to break like 6 times to make buying one of these worth it?

Actually this is a replacement cuz the microUSB port on my old one is very loose now, hard to get it to charge. But it's been good for 2-3yrs.

The cells inside are still good... Just the connection really...

Just buy xiaomi powerbank. Got mine 20Ah for 22€ in local store and you will be sure it is not crap

Yup, Xiaomi has good reviews and price to performance ratio.