smartphones have become our daily life
companion and we need more and more
battery life mostly a full charge is not
enough for a day if you have the user
the easiest way to expand your battery
life is a power bank but which one
should you buy if you check out power
banks on Amazon then you can find a lot
of mixed reviews many reviews are paid I
know that from my experience and some
reviews are just from people who have no
idea what they're talking about so most
people just search for the biggest
capacity advertised for a low price but
this is something you should not do and
the reason is that sellers mostly lie
about the capacity the first let me
explain how a power bank works and why
you can't simply divide your power banks
capacity by a sound battery capacity and
get the charging cycles so there are
different kind of power banks with
different battery technologies on the
inside cheaper power banks use
lithium-ion cells especially the
affordable 18 650 cells they are cheaper
and they have six sizes but well that's
the only advantage they have a higher
discharge rate just to get hotter and
are not really durable compared to the
new lithium polymer cells
however Lipa power banks more expensive
and also harder to get but they are
smaller and more durable on the long run
also the Liam ion batteries can catch
fire more easily because of their fluid
electrolyte Lipa batteries instead they
use a solid or gel electrolyte and a
more safe well I know it's not very
realistic that the power bank will catch
fire but safe safe and here's a quick
video I recorded two years ago and
imagine your power bank gets shorted and
blows up like a note 7 and that's not
really funny now let's talk about the
actual capacity because he it gets
tricky power banks get to 99% produced
in China and most cheap unknown
manufacturers of OM data sly about the
battery capacity you can't imagine how
many emails I get every day of power
bank sellers and they want to sell me
the latest product but I just see the
first looked at so that's a fact
but although the capacity advertised is
not
the actual capacity that goes into your
sounds battery
so first the capacity inside is measured
as mah that stands for milliamp hours
and tells you how many milliamps or amps
you can drain from the battery in one
hour so for instance a 10,000 milliamp
hour battery means you could drain
10,000 milliamp to 10 hours for one hour
or for instance um 1,000 milliamps for
ten hours but you can only do this at
the rated voltage of the cells and most
cells are rated at 3.7 volts if you
multiply a million dollars and the rated
voltage you get the actual energy which
would be three point seven watt hours
that means you can drain three point
seven watts for one hour from the
battery but why do we need to know all
that so you need to know that USB ports
are made to operate at five volts so you
always plug it smartphone into five volt
source this is the output of the normal
USB port of your notebook or phone
charger so inside of the power bank the
voltage has to be stepped up from the
three point seven volts to five volts
using a boost converter this conversion
is not lossless that means there is a
conversion loss to calculate the root
capacity take the advertised power bank
capacity times three point seven and
divided by fire this is now your real
capacity and it's always lower than the
advertised one the second factor is the
efficiency factor and this one depends
on your power bank cheaper banks have a
bad convert inside that transforms a lot
of energy into heat which is lost high
quality power banks have better up
stepper resulting in a small loss so
good power banks lose here let's say 50%
some you in 20 or way more now let's do
the math your 10,000 mah power bank at
frequent cell walls actually can only
supply seven thousand four hundred
million dollars at five volts and if the
converters crap then maybe even less and
maybe in a couple of months even more
less because it sounds alter so if you
thought that you could charge your 2000
mAh not found five times with
10,000 NH battery then you know
disappointed because it just has 5900 MH
coming from with power banks use B port
and there is another conversion in your
smartphone back to 3.7 volts so this
advertised 10,000 mah power bank will
charge a smartphone only around 2.5
times
What you should know before buying power banks ?
Smartphones became part of our life
We use to talk, play games,
listen music, watch videos & lot more
Eventually, all these drains the smartphone battery
Therefore, to charge we use portable power bank
so that it can charge our mobile
for N number of times
depending upon the power bank capacity
After buying the power bank,
one can probably get these questions
How many times that this
power bank can charge my mobile?
Does this power bank contain same
capacity as advertised in the label?
This video will answer all your questions
and also the marketing strategies
behind the power bank
Here, we gonna we about the power bank specifications
Consider that I am using a power bank
of capacity 15,600mAh
Let's remove the front plastic case
to see what is inside the power bank
Normally, it contains two major parts
The circuit named battery charging board
and the parallel connection of battery cells
These cells are Lithium-ion 18650 cells of 3.7volt
with capacity ranging from 2,000 to 3,000 mAh
In my case, it is 2,600 mAh
While in parallel connection of these six cells,
the total capacity is the sum of each cell
Thus, the rated or advertised capacity
of this power bank is 15,600 mAh
with same voltage of 3.7V
But for USB charging, the smartphone needs the
power with voltage of 5V
So, this board in power bank
converts 3.7V to 5V for smartphone
This process is known as Boost converter
Therefore, the rated power bank capacity get reduced
due to this voltage conversion
To find the USB output capacity,
we need to multiply the rated or
advertised capacity with 3.7V
and then divide it with 5V
For this power bank of 15,600 mAh capacity
is equal to 15,600 * 3.7 divided by 5
is equal to 11,544
Thus, the USB output capacity is equal to 11,544 mAh
Also, we have to consider the losses like
Conversion loss, losses in USB cable
and losses in phone charging circuit
which produces heat
This reduces the power bank efficiency
For a good or new power bank,
the efficeincy is 90%
For average or old power bank,
the efficiency is between 70% and 90%
So, the actual capacity of the
power bank is obtained by
multiplying the USB output capacity with
efficiency of 90% or by factor 0.9
11,544 * 90 divided by 100
is equal to 10,390 mAh
This gives the actual capacity for charging smartphones
For finding N number of
full charges for smartphones
N is equal to actual power bank capacity
divided by mobile battery capacity
Considering 3,000 mAh as
average mobile battery capacity
So, N is equal to 10,390 divided by 3000
is equal to 3.46 times
Here, 3.46 is the number of times
that power bank can charge 3000 mAh battery
Finally, the marketing strategies behind the power bank
When you notice the specifications
label in the power bank
You can only see the rated capacity in mAh for 3.7V
rather than actual capacity for 5V
Power bank manufacturers advertise
the rated capacity in 3.7V
which is larger and can attract more customers
It is genuine in their own way
So, it's us customers who need
to calculate the actual capacity
There is also an exception
This chinese power bank mentions
rated capacity in 3.7V
with actual capacity in 5V
and also claims its efficiency
has greater than 90%
This case is rare, really very rare!
To calculate for your power bank and smartphones,
Use these formula
Replace advertised capacity
with your power bank capacity
Then, find USB output capacity and actual capacity
Also, replace the battery capacity
with your mobile battery capacity
Then, find number of full charges