# How to make a discharge curve

I am trying to make a discharge curve for one of my batteries that I have. All I know about it is that it is a 1.5V battery. Now if I have to make a discharge curve for it, how would I make one and what load should I use to make one? Should I pick a load with a rating of 1 C? but I don't know how to calculate this 1 C value (of the load) based on my battery.

I am very new to this topic. Any help is appreciated.

Thank you so much!

## 1 Answer

Using a constant current load you'll get a nice curve if you plot the voltage over time.

The C rating is given by the manufacturer as an indication of the safe maximum constant current draw from the battery.

Some searching turned up that it is standard to make the discharge curve over 20 hours. So this would be like 0,05C. I speculate that this will avoid some thermal effects, Because your battery would probably get hot from a 1C discharge.

If it is a AA battery, set the current to about 100mA. AAA - 50mA if it is another kind of battery, guess or measure how much more or less volume it has compared to the AA battery, and factor that into the current. It is just a way of guessing capacity. So if the battery looks 4 times larger than a AA, set the current to 400mA.

You can do this guessing because battery capacity is proportional to volume. After you've done this, you have measured the capacity of your battery, and you can make more precise measurements. Good luck

• ok, so the load that I will set for this battery will be proportional to the capacity? So say if a AA battery has a volume of 20 cm3 and my battery has a volume of 1 cm3, then my load would be 5mA, right? And would I connect this 5 mA load to my battery? – user5139637 Aug 3 '15 at 14:47
• Another question I have is (for the x-axis), how will I measure the amp-hour. Thank you so much for your answer – user5139637 Aug 3 '15 at 14:56
• @user5139637 The amp-hour is simply the constant current of the load multiplied with the time ( in hours) that it took for the battery to drain. Yes to your other questions. – user55924 Aug 3 '15 at 15:04
• Would an LED count as a constant current load? Or would a resistor? – user5139637 Aug 3 '15 at 22:20