In this Instructables let's find the capacity of Fake 10400mAh Power bank.

Previously I used This power bank to make my own power bank because I bought it for $2.

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So let's get started

## Step 1: Opening

Let's first open the power bank

One's we have opened it cut the wires of power.

since there are 4 batteries and the total capacity is 10400mAh so the capacity of each battery is 2600mAh

## Step 2: Charging

Battery was not fully charged so first charge.

let's first charge them using TP4056 module

## Step 3: How to Calculate Capacity

We can simply use 1ohm 5 w resistor in series with the battery to test the capacity

but, voltage will decrease over the time and so our current ( resistance will be 1ohm)

and in this case we need to use integral function which is quite inaccurate

## Step 4: LM358

Since using integral will be quite inaccurate let's use constant current source.

we can built a constant current source using LM358

let me explain how it works

1) When Vin is higher then Vref output is high which turns our MOSFET On

When MOSFET is trued on there is voltage drop across the resistor and our Vref is now High

2) When Vref is higher than Vin Output is Low and this cycle repeats

## Step 5: Capacity Test !

One's the circuit is done adjust the potentiometer to get the current of 1A

It took 15 min for the battery to discharge completely.

## Step 6: Calculation Time

Alringht so the,

Current was 1A

and time was 0.25 hr

so the capacity of the battrey is.....

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250mAh

## Step 7: My Thoughts !

I think they forgot to divide Every thingby 10

Because Actual capacity of the Power bank 1000mAh and not 10400mAh

And

The capacity of battrey is 250mAh and not 2600 mAh

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(If there is Any Mistake Please feel free to tell me in comments)