For Redmi Note 4 which has 4100 mAh Li-Polymer Battery, now Mi has it's own power banks, -
10000mAh Mi Power Bank 2 & 20000mAh Mi Power Bank 2
which one should I buy?
does the latter charges at double speed saving time?
I'm new to Poweerbanks.
larger power banks do not charge fast. they have more battery capacity so you can charge your phone(s) more times.
for fast charging... check if your phone has quick charge support. if yes, get the mi 20,000 version as 10,000 version does not have quick charge support.
hard to say. i got it because i needed usb-c rapid charging. it does the job. it is one of the many brands that seems to be based in china with offices in usa. like choetech. anker and aukey are probably slightly more reputed. but all of these companies have made shitty usb-c products so in the end it depends from one product to another.
but as with any usb-c product... it is hard to know if it is fully spec compliant.
it seems to work well and also worked fine with the amazonbasics usb-c cable with chipset. my anker powerport charger did not work with that cable. because it is not fully spec compliant. i am using google's cable on the anker charger which does work.
i got tronsmart largely because it was the only good option in the reasonably priced segment. today it is not. i am glad i have a unit which should last me for a while. because mi and OnePlus are still not launching usb-c power banks in india.