Thanks for the reply.

Assuming that the powerbank is made of multiple cylindrical batteries output at 3.7V, the powerbank consolidates the output of each battery into one main output, the USB interface, which discharge at 5V. Hence the formula used above, correct ?

I have a YooBao YB-645 which claims to have the capacity of 8800mAh. The Input was stated as 5V/1500mA and the output was stated as 5V/1000mA.

So based on what I understand so far,

a) 8800mAh * 3.7V = 32,560 then 32,560 / 5V = 6,512 mAh is the ACTUAL capacity (assuming 100%).
Further Questions :

1) Is 100% output capacity a reasonable expectation for NEW powerbanks or is it by nature not possible ?  (Kinda like buying a 1TB HDD is not possible to get *exactly* 1TB space inside)

2) Input basically just tells you at what rate it is charging the power bank, rite? It doesn't in any way change the total capacity of the powerbank since the capacity is already fixed, right ?

Part 2: So called 20000mAh powerbank test

i had borrowed 20000mAh powerbank from my friend. Due to warranty reason, my friend not allow me to open it.
tried some method to figure out how many 18650 battery inside the powerbank, lastly i use torch light and saw there are 6 18650 battery.
What is the capacity of each 18650 battery i'm not sure, but i can test and prove it.



Written 20000mAh, made in Taiwan
Written 2 output current: 2.1A and 1.0A. After i tested, it is just a parallel output from same source, not separated.

This set up is similar with my part 1 test, using 2 10ohm resistor in parallel, resulting 5ohm resistance.
Output current stable: 4.79V, 0.94A


Result are recorded, total discharge time is 4 hour 40 minutes. Total output power is 21.01Wh, only 28.4% is the REAL output power.
Rated capacity is 3.7V X 20000mAh = 74Wh (vs 21.02Wh Real)

[My tested PN-910 had discharged for 7 hour and 20 minutes, total output power is 34.13Wh, 82.4% is the REAL output power]
Rated capacity is 3.7 x 11200mAh = 41.44Wh (vs 34.13Wh Real)


The 20000mAh powerbank had been tested for twice because the first time test i had over estimated it can discharge for at least 5 hours.
But it is actually less than 5 hours.

Dimension measurement by vernier calipers（20000mAh）：135mm x 71mm x 24mm
(my friend said this unit was selling with price tag of RM110)

Is anyone using this? I am afraid I get cheated, because this power bank cost me RM150.
I am using Edvan 8400mAh, but I am not sure whether this power bank is consider good or bad.

There are so many brands. Why don't you try and see how many times it can charge your phone. You take 8400 and consider 75% as real capacity.  If it charges your phone sufficiently up to this rating you should be fine.

my yoobao yb-642 is slowly dying on me, am wondering if constant exposure to heat will damage it? i always keep it inside my car's dashboard.

There are so many brands. Why don't you try and see how many times it can charge your phone. You take 8400 and consider 75% as real capacity.  If it charges your phone sufficiently up to this rating you should be fine.

Do I need to use my handphone and power bank from fully charged until the battery totally plat? Because I am afraid it will destroy my handphone aand power bank battery if I do it this way.

Lithium batteries should be recharged froyo about 10% from what I've read all over.

I always charging my phone while I am playing game.
I may need to test it out one day thanks a lot for your reply.

Heat is bad for batteries. Keeping it in the glove compartment will be a little better but how do you charge it?

2800mah x 3.7V / 5V = 2072mah..
should be able to charge ur phone at least one times with phone off..
if on wifi, play video etc while charging, wont fully charge of course.

powerbank mah times nominal powebank battery output, 3.7V, divide by its output voltage which is 5V..

simply said, the 2800mah is at 3.7V,
if change voltage to 5V, mah will drop..

yes usb is 5V but it's also charging a lower volatage 3.7V handphone battery.. so means MAh will increase back..
so just compare powerbank capacity with handphone battery since both is 3.7V type , of cos with some conversion losses..

cannot say like that, charging voltage must higher than batt voltage, if not, no potential difference, no flow..
no such increase back.

what you toking.. if battery is 3.7V use direct 3.7V charger lor..

if use USB 5V charger, there is already a step down circuit in your phone.. you think plug terus 5V into a 3.7V battery?

charger output is 5v 1A

and you think 5V from the charger goes directly into the phone battery?

yes, charging voltage must higher than charged device.
after the charged device obtain its full charging capacity or at certain limiting voltage, there will be cut off mechanism.

same as charging car battery, charger is at 16V.
car battery where got 16V nominal?