Picture of Laptop Battery Analyzer /Recycler
I started out , when at work they had pile of battery packs for laptop computers , that no longer worked. Well I know that most (not all ) Battery packs for Laptops are made up of a bunch of 18650 Li-Ion Battery Cells , and it is usually only one or 2 cells that go bad in a Pack making the entire battery pack no  good. So I grabbed a Bunch of them and took them apart. My use was going to be to use them to power some Bicycle lights. Figured I would charge them up and shouldn't be too hard to find the bad cells using an Volt/Amp Meter , this Worked but not well by any means ,I  soon discovered that a lot of the cells would take a charge , but not much of a charge , found this out the hard way with bike lights that went dark too fast.

So I came up with this Idea of using a Computer , with an analog input, and would read the out put of the battery across a load over time to determine how much energy the battery cell could store.   My first attempt was using an old PC with a Metrabyte DAS-8 A/D board . It was basic , I would manually connect the load start teh data collection, stop it after time , and then using excel determine the amount of energy in the Cell.  But I wanted to do this more automatically . I was using an Ardunio for another project ( which will soon have an instructable for it )  and realized it had all that I needed to do this . so I made the switch and it was a lot easier to wire up , program and took up a lot less space.
Remove these adsRemove these ads by Signing Up

Step 1: Charging The Batteries

Picture of Charging The Batteries
Charging LI-Ion Batteries
when charging LI-ION batties Be careful! they can be unstable and catch fire. I have never personally had this happen , but I don't care i always take the precautions, better safe then sorry. there are plenty of horror stories out  there. 
1) Never Charge unatteneded!
2) Charge out doors or some place some place pretty much fire proff ( I charge mine on the Bricks of my fire place or top of  Steel sheet )
3) AVOID drivect shorts
4) do not use a Physically Damaged Cell.
5) Dispose of Properly ( I take my To Home depot and deposit in there battery recycling bins )    
Most of the time I use  this simple charger from Deal Extreame ( http://dx.com/digital-li-ion-18650-battery-charger-6105)  I also will use a larger RC  Smart charger for doing multi cell packs , but that is a little beyond what this Instrucable is for.

Step 2: Parts List

Picture of Parts List
 Parts List
- Adrunio Uno  or compatible ( ebay $20  )
- 16 X2 LCD display that uses a Hitachi HD44780 driver, They are very common, I have gotten several  from old HP servers and Rolm Phones, but one can Be purchased here. for $10 http://www.adafruit.com/products/181
- An opto 22 Solid State Relay ( RED , 5 Vin )  I happen to have  an ample supply around my basement
- 18650 battery Holder , $2 eBay
-10 M ohm  1/4 watt Resistor (  or something large just to be used as a Pull down )
- 4 Ohm 6 watt  Resistor
- 1 push Button, momentary contact  switch (not Shown )
-  6  to 10 V 500 ma , Power supply , Wall wart style to power the adrunino (not Shown) 

Step 3: Theory and operation

Theory and Operation

Li-Ion Batteries , when charged under no load have a Voltage of about 4.2 Volts , that quickly drops to about 3.9 Volts under load and slowly drops as the charge is used . a Li-Ion Battery cell is considered fully discharged then the under load Voltage get below 3.00 Volts.
So what i do it have the battery attached to one of the Adruino's Analog Input's , and read the No-load value. at the same time waiting for the start Button to be pressed. If the voltage input is above 3.00 volts when the Button is pressed the test will start. 
When the test starts  the Solid State relay is energized with switch the 4 ohm resistor to be a load directly across the battery. the Voltage is then read every half second and using ohm's Law current ,  I=V/R,  R= 4 ohms and V is read from the Analog input. Since this reading is taken every half second , we know there are 7200 1/2 seconds in an an hour , we just take the current  multiply it by 1/7200 of an hour and accumulate all those reading and until the Voltage  is below 3.00 volts , at that point the Relay is shut off and the grand total of how many maH of energy was released is displayed

Step 4:

Picture of
4) After getting the parts together First thing to do is prep and connect the LCD dispaly , I used the basic setup of an LCD display as seen  on the Ardunio tutorial page ( http://arduino.cc/en/Tutorial/LiquidCrystal ) I however do not use a Potentiometer for brightness control, I just connect Pin 3 to Ground . I also Do not use the same Pins. I don't use the High end Pins, because i had ideas of putting an Ethernet/SD card Shield on and recording the data from each Battery as it was being tested , that however has not come to fruition .

back to the matter at hand the LCD display .
Pin   Destination
1   - GND
2    + 5
3       GND
4   -  Digital Pin 2
5 -     Digital Pin 3
6,7,8,9,10  No connection
11   - Digital Pin 5
12  -  Digital Pin 6
13 - Digital Pin 7
14    Digital Pin  8
15     + 5  
16 -- GND 
that will take care of wiring the LCD

Step 5:

Picture of
next I take the Battery Holder . I attach the negative to Ground , and the Positive to Analog Input 0 .
Between  the analog 0 input and ground i put a 10 M ohm resistor . I use this as a Pull down resistor, helps elivate noise especially when there is no cell in the holder .
Next I take the Solid state relay , attach the input "-" to Ground, and the input Positive to Digital Pin 1 . now I take the Positive ( If your SSR has  polarity on the output some do some don't )  output Pin of the Solid state relay and attach it to the Positive terminal , and  between the Negative terminal and Ground put the 4 Ohm 6 Watt Resistor , this will be the load resistor and give it some space because it can get hot.

finally attach a Push button between +5 and digital Pin 0  ( I actually use a SPDT  ) Push button and attach the other pole to ground , that can cause a Noise spike to trigger it, or you could just use another 10 M ohm resistor as a pull down it will work too. I know its overkill, just a habit from years of work.

that Completes the wiring , next is he code and here it is . Because I'm using Pin's 0 and 1 , you might have to disconnect those to pins while you down load the program , other wise it might not load.

Step 6: The source Code

Picture of The source Code
Here is the source code for the Analyzer 

A battery life cycle tester using an Lcd as output  

// include the library code:
#include <LiquidCrystal.h>

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd( 2, 3, 5, 6, 7, 8 );
const int buttonPin = 0; 
int sensorPin = A0;    // select the input pin for the Battery
int sensorValue = 0;  // variable to store the value coming from the sensor
const int relay=1;
int buttonState = 0;
float mah = 0.0;
long timestart  ;

void setup() {
  // set up the LCD's number of columns and rows:
  lcd.begin(16, 2);
  // Print a message to the LCD.
  lcd.print("Battery life tester");
  pinMode(relay, OUTPUT);
pinMode(buttonPin, INPUT);

void loop() {
  // set the cursor to column 0, line 1
  // (note: line 1 is the second row, since counting begins with 0):
  digitalWrite(relay, 0 ); //set the LED-relay off
  while (buttonState == LOW ) {
  sensorValue = analogRead(sensorPin); // read the battery
  //  the voltage
  buttonState = digitalRead(buttonPin);
//  if (buttonState == HIGH) {
//    if (bb > 0) { bb=0; } else { bb=1; }
//  }
  lcd.setCursor(0, 1);
  lcd.print(" Volts");
  } //end get ready loop 
  digitalWrite(relay, 1 ); //set the LED-relay on
  lcd.setCursor(0, 0);
  lcd.print("Testing              ");
  lcd.setCursor(0, 1);
  lcd.print("                         ");
  mah = 0.0;
  timestart = millis( );
  while ( ((sensorValue*4.98)/1023) > 3.00 ) {
     lcd.setCursor(0, 1);    
     lcd.print(" V ");
     sensorValue = analogRead(sensorPin); // read the battery
     mah = mah + (((sensorValue*4.98)/1023)/4 )/7.2;
     lcd.print(" mAh ");
     delay ( 500 ) ;
     lcd.print((millis( )- timestart)/1000); // time since test staarted
  } // end battery drain
    digitalWrite(relay, 0 ); //set the LED-relay off

  // final results
   lcd.setCursor(0, 0);
   lcd.print(" mAH ");
   lcd.print((millis( )- timestart)/1000);
   lcd.print(" S ");
   buttonState = digitalRead(buttonPin);

Step 7: Run it

Picture of Run it
First put a charged battery In the Holder .  Note the voltage  above 3.0 

Step 8: Out the battery under load

Picture of Out the battery under load
Press the start button and watch and Wait. On top displays the seconds that have elapsed  83 seconds in this case 
the current voltage reading ,3.64 Volts , notice how much it dropped under a 1 amp load. and finally how much energy in Millamp Hours has been discharged, 21.06 Mah .

Step 9:

Picture of
And when it completes , the Top line has the total Energy that was in the cell, 629.24 Mah  and how long it took, 2788 seconds or 46 Minutes and 28 seconds. in this case this is not a battery I would keep . I don't keep any under 1000 Mah,. and  it has reset it self just waiting for you to press the button again and start the test going again.   

Step 10: What I'd still Like to do .

I would like to record the data Points to an SD card and then have the data accessible from a Web page through an Ethernet Shild ,  thats Why I didn't use Pins 4, 9, 10, 11, 12, 13 they are used for the ehternet/SD shield. but that is for a later time.
mkhan8129 days ago
Is there any limitation on the resistor used ? i am using a 5.6 ohm 10 watt resistor ... i read in a similar project that the resostance should be less than 4 ohm ... please clarify
TimoM8 months ago

I just can get an 3.9 Ohm 9W resistor.
I'm right that I must change this line

mah = mah + (((sensorValue*4.98)/1023)/4 )/7.2;


mah = mah + (((sensorValue*4.98)/1023)/3.9 )/7.2;
or is there something else to change?

I=V/R so I = sensorvalue (V) / Resistance (Ohm)

You are right. For more precision, check the total resistance of your circuit with a multimeter and use this value in your program.

Roger Gaudreault made it!9 months ago

It works! Now I will check my diving lamp batteries... I'll soon solder all parts to a prototype board and use it regulary. Thank you all.

ps: I removed the push-button switch and added a buzzer. :)


I'm building this project, and I have the same problems than tony_roti. I'm wondering: Do we absolutely need a push-button switch? All my problems seems to come from here. I will modify the program to start automatically when the voltage is above 3.00 volts. Thank you splats for this nice project and all others for your constructive comments.

Does this work for 26650 batteries too? They basically have the same voltage, and just more mAh than 18650.

tony_roti1 year ago
I think that you must put a lcd.clear(); before final result are printing. And delete spaces in lcd.print(" V "); and lcd.print(" mAh ");
Why? Because if you test a cell with bigger capacity (4 digits), you won't be able to read the final digit of timing.
tony_roti1 year ago
I was wonder if it can be adapt to measure the capacity of Ni-Mh/Ni-Cd 1.2V cells? In that case the load rezistor must be 2.8Ohm if we want a 500mA discharge current right?
I think the safe discharge voltage for this tipe of cells is 1Volt.
tony_roti1 year ago
It's working great. Fantastic job. I have tested several god and bad cells. Especialy one that came with a cheap chinese flashlight, that says 4200mA, after I tested it, has only 729mAH.
Thank you splats for sharing.
tony_roti1 year ago
Hi splats! Great idea. I have placed everything in order but I still have 2 problems (one solved):

1. Wrong or no Initialization of the display: My LCD consistently showed black boxes in the bottom line. I've made some changes to fix this: since I don't read from the display, I've put the pin 5 of the display (RW) to the ground and use pin 4 (RS) and 6 (E) of the display for LCD initialization. I did use a potentiometer for brightness control and a 10Kohm resistor on pin 15 of the LCD for dimming the light of the display. I left everyting else in place like you did. Problem number one solved.

2. If no battery is inserted, the sistem displays for a short period of time "Batery life test" and goes directly to final result printing 0.00 mAh, 0s, 0.00 Volts (image no. 1). The relay in this state is off but at every two seconds, the relay is on for a short period of time (miliseconds). If a battery is inserted, the relay goes directly in high state and the sistem goes into the testing mode (image no. 2). This part seems to work well untill the 3V is reached. After that it shortly shows the final result and enter again in testing mode (loop mode - see the video). I have used this relay brick with built in EMF protection: http://www.parallax.com/product/27115. I have put the - IN to gnd, the + IN to 5V and the S pin (signal) to Arduino digital pin 1. The button is conected to Arduino digital pin 0 but it seems that the sistem ignore that. The load resistor in on NO (normaly open) OUT PIN of the relay. I don't know what the problem is.

3. Why do you put the buttonPin on 5V instead of the GND?
Thanks in advance.
Problem number 2 solved. I have used a 10Mohm pull down rezistor for the button. It seems to work fine now.
aLV4261 year ago
Hi Splats - thanks for the feedback! I suppose I should mention you should place an EMF protection diode across the coil of the relay, I can't get over how low the component count on this project is - good work Splats and thanks for sharing!
splats (author)  aLV4261 year ago
SInce I'm using a Solid State Relay , I don't have to worry about back EMF. but if I was powering a straight Relay coil then yes .
aLV4261 year ago
Great idea! Can you help with the relay choice? Does it have to be solid state?
Would this make a good choice?
This is rated @ 8A

This is a standard coil based relay:
I ordered 5V Relay Module for Arduino from dx, rated 10A AC/DC:
I don't know if the relay must be solid state. I think it should work with any 5V relay.
I will see. I'm still waiting for my order to arrive.
splats (author)  tony_roti1 year ago
No it doesn't have to be solid state. I just used one because I have about 100 of them in a drawer. it should work fine with that relay.
splats (author)  aLV4261 year ago
No it doesn't have to be solid state. I just used one because I have about 100 of them in a drawer.
tony_roti1 year ago
I just ordered most parts from dx (Funduino uno R2 compatible - USD$ 12,99, 16x2 LCD display - USD$ 3,40, 5V relay - USD$ 2,20, and some printed circuit board breadboard and jumper cable wires, total USD$ 24,79). Because it takes a lot of time to come (about 40 days), I will write after I put all parts together. I hope it will work.
hedonistic2 years ago
This is a little beyond my knowlage and skill set but I would love to have an 18650 tester. Do you know of any low cost options, or where I could go to have one built?
technitute3 years ago
hey its a great post to teach me buil the technology.
please also share this post here for me please:- http://technitute.com
joen3 years ago
I hope this doesn't sound like a "not nice" comment but you seem to be as spell challenged as I am.(I misspelled about 10 words in this comment alone!) There are a number of words that are just spelled wrong and others that are spelled right but are the wrong word for what was obviously intended.

It is a great instructable but all the misspelled words were rather distracting. I would suggest doing what I do and that is use a word processor program that has a spell checker and correct any misspelled words before copying and pasting your text into the instructable.

This instructable is a little advanced for me but I am keeping it for when I can catch up to it.

Thanks for the idea!
splats (author)  joen3 years ago
None Taken , I went back in an cleaned it up a bit . I just type too fast for my own good sometimes.