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Nowadays fake Lithium and NiMH batteries are everywhere which is sold by advertising with higher capacities than their true capacity. So it is really difficult to distinguish between a real and a fake battery. Similarly, it is difficult to know the capacity retained in the salvaged 18650 laptop batteries. So, a device is required to measure the true capacity of the batteries.
In the year 2016, I have written an Instructable on ” Arduino Capacity Tester - V1.0 ” which was a very straight forward and simple device. The earlier version was based on Ohms Law. The battery to be tested is discharged through a fixed resistor, current and time duration is measured by Arduino and capacity is calculated by multiplying both the readings ( Discharge current and time ).
The drawback of the earlier version was that during the testing, as as the battery voltage decrease, the current also decreases which make the calculations complex and inaccurate. To overcome this, I have made the V2.0 which is designed in such a way that the current will remain constant throughout the discharging process. I made this device by inspiring the original design by MyVanitar
The main features of Capacity Tester V2.0 are :
1. Capable of measuring the capacity of AA / AAA NiMh / NiCd, 18650 Li-ion, Li-Polymer, and Li FePO4 battery. It is suitable for almost any kind of battery rated below 5V.
2. Users can set the discharge current by using the pushbuttons.
3. OLED user Interface
4. The device can be used as an Electronic Load
Disclaimer:Please note that you are working with Li-Ion battery which is highly explosive and dangerous. I cannot be held responsible for any loss of property, damage, or loss of life if it comes to that. This tutorial was written for those who have knowledge of rechargeable lithium-ion technology. Please do not attempt this if you are a novice. Stay Safe.

Components Used
1. Arduino Nano
2. Opamp LM358
3. 0.96” OLED display
4. Ceramic Resistor
5. Capacitor 100nF
6. Capacitor 220uF
7. Resistors 4.7K & 1M
8. Push Button
9. Screw Terminal
10. Prototype Board
11. PCB Stand-off
12. Heatshrink Tubing

Tools Used
1. Soldering Iron
2. Clamp Meter
3. Multimeter
4. Hot Air Blower
5. Wire Cutter
6. Wire Stripper”

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