Measuring Internal Resistance of Batteries
Shawn Hymel 
Introduction
Batteries are incredibly useful devices for transforming chemical reactions into electrical energy. We use them every day in things like flashlights, cars, video game controllers, and so on. To learn how batteries work, check out the following video:
To get a more in-depth explanation of batteries, see this article:
What is a Battery?
May 3, 2016
In this tutorial, we will make a crude battery out of a lemon, a zinc-plated screw, and a copper-plated coin. The metals in the screw and the coin react with the acid in the lemon to create a flow of electrons.
Lemons, in reality, make for poor batteries. One reason is that the zinc continues to react with the lemon without a circuit present. This means that the battery would only have a shelf life of a few hours.
Another factor is the internal resistance of the lemon battery. We will discuss internal resistance in the next section and why it is important for batteries.
Required Materials
- Lemon
- Zinc-plated nail or screw
- Penny (or other copper-coated piece of metal)
- AA battery
In addition to these materials, you will need a way to measure voltage. A multimeter will offer the best accuracy, but you can also build your own voltmeter from parts found in the SparkFun Inventor's Kit.
If you want to build your own voltmeter, here is what you will need:
Tools
In addition, you will need a hobby knife to cut a slit into the lemon.
Suggested Reading
Before continuing with this project, we suggest you be familiar with a few concepts:
- Voltage, Current, Resistance, and Ohm's Law
- What is a Circuit?
- Series and Parallel Circuits
- Voltage Dividers
- How to Use a Multimeter
- Analog to Digital Conversion
- What Is a Battery?
- SIK Guide: Reading a Potentiometer
- SIK Guide: Using an LCD