Advanced lab
How Do Batteries Work?
- Grades 5-8
- 45 minute lab
- NGSS 4-PS3-2, MS-PS1-2
Quick answer
A battery stores energy in chemicals. Inside, two different materials sit in an electrolyte. A chemical reaction makes one side give up electrons, and those electrons flow out through the circuit to the other side. That flow is the electricity that lights an LED. You can even build a working battery out of salty play dough, a nail and some copper wire.
The three parts of every battery
Every battery, from a tiny watch battery to a car battery, has the same three parts:
- Negative electrode (-): a material that gives up electrons easily, like zinc.
- Positive electrode (+): a different material that takes electrons in, like copper or manganese dioxide.
- Electrolyte: a paste or liquid full of charged particles called ions. It lets the chemical reaction happen and lets ions move between the two sides.
A thin separator keeps the two electrodes from touching inside the battery. The electrons cannot cross the electrolyte, so the only way for them to get from the negative side to the positive side is the long way around: through your circuit.
Why do batteries run out?
A battery does not store electricity like a tank of water. It stores chemicals that are ready to react. As the battery powers a circuit, the reaction slowly uses those chemicals up. When they are gone, the reaction stops, and so does the electricity. Rechargeable batteries can run the reaction backward when you plug them in, rebuilding the chemicals for next time.
Volts: how hard a battery pushes
The voltage of a battery tells you how hard it pushes electricity around a circuit. It depends on which two materials are inside, not on how big the battery is. A tiny AAA and a big D battery are both 1.5 volts. The bigger battery just has more chemicals, so it lasts longer.
- One AA battery: 1.5 volts
- A Squishy Circuits battery holder with 4 AA batteries: 6 volts
- A car battery: about 12 volts, from 6 cells of 2 volts each
- One dough cell with a nail and copper wire: about 0.8 volts
Stacking cells in a row, called series, adds their voltages together. That is how the battery holder turns four 1.5 volt batteries into 6 volts. Learn more in Series and Parallel Circuits.
Make a battery from play dough
A galvanized nail is coated in zinc. Push one into salty dough with a piece of copper wire and you have the same three parts as a real battery: zinc for the negative side, copper for the positive side, and salty dough as the electrolyte. One dough cell makes about 0.8 volts, which you can measure with a multimeter.
Try it with dough
Build a Squishy Battery
One cell is not enough to light an LED, so you will join six cells in a row. This lab works best for older students or with an adult helping, since it uses nails and wire.
You need
- 6 or more galvanized nails
- Bare copper wire, cut into 6 or more short pieces
- Conductive (salty) play dough
- White insulating dough
- 1 red LED
- Multimeter (helpful, but optional)
Steps
- Make one cell: push a galvanized nail and a piece of copper wire into a ball of conductive dough. Do not let them touch.
- If you have a multimeter, set it to DC volts. Touch the red probe to the copper and the black probe to the nail. You should see about 0.8 volts.
- Make electrode pairs by twisting the end of a copper wire around the head of a nail.
- Make six blocks of conductive dough and line them up with a thin wall of white insulating dough between each block.
- Bridge each white wall with an electrode pair: the nail goes in one block and the copper goes in the next. Keep every pair facing the same way, so each block ends up with one nail and one copper wire.
- Add a plain copper wire to the first block and a plain nail to the last block. These are your + and - ends. Measure the whole battery: it should be about 4.7 volts.
- Push the long leg of a red LED into the dough at the copper (+) end and the short leg into the dough at the nail (-) end. Turn off the lights and look closely.
What happens
Each cell adds about 0.8 volts, so six cells in series make about 4.7 volts. That is enough to light a red LED, though only dimly: the dough battery can push hard enough, but it cannot supply much current.
Not working?
No voltage? Make sure you are using conductive dough, not white insulating dough, and that every cell has two different metals. If the total is low, check that all the pairs face the same way. Red LEDs need the least power, so start with red.
How the cells add up
Each nail-and-copper bridge connects the negative side of one cell to the positive side of the next, so the cells push in the same direction, one after another. That is a series connection, just like the batteries inside the battery holder.
Want more current instead of more voltage? Build two batteries and connect them side by side, + to + and - to -. That is a parallel connection. Can you make enough cells to beep a buzzer or spin the motor?
Battery safety
Do
- Have an adult cut wire and handle sharp nails
- Wash hands after handling galvanized nails
- Recycle used batteries where you live
- Take batteries out of toys you are not using
Don't
- Never cut open or heat a store-bought battery
- Never put batteries, especially button batteries, in your mouth
- Never mix old and new batteries in one holder
- Never connect a battery's + and - ends with a bare wire
Key words
- Battery
- One or more cells that turn stored chemical energy into electricity.
- Cell
- One set of two electrodes and an electrolyte. A battery can have one cell or many.
- Electrode
- One of the two materials in a cell. The negative electrode gives up electrons and the positive electrode takes them in.
- Electrolyte
- A paste or liquid full of ions that lets the chemical reaction happen. In a Squishy Battery, it is the salty dough.
- Anode
- The electrode that gives up electrons. In a Squishy Battery, the galvanized nail.
- Cathode
- The electrode that takes in electrons. In a Squishy Battery, the copper wire.
- Voltage
- How hard a battery pushes electricity around a circuit, measured in volts.
For teachers
At the galvanized nail, zinc is oxidized: each zinc atom becomes a Zn2+ ion and releases two electrons, which makes the nail the anode and the negative terminal. The electrons travel through the external circuit to the copper, the cathode and positive terminal, where they are used in a reduction reaction with hydrogen ions or dissolved oxygen in the salty dough. The copper itself is not used up. This is a voltaic cell, the same idea as Alessandro Volta's first battery in 1800 and the classic lemon or potato battery.
The voltage of each cell depends on the pair of metals, not the size of the cell. Bigger electrodes and fresher, wetter dough give more current. The dough cell has a high internal resistance, which is why the LED is dim even at 4.7 volts. Students can explore this with Ohm's Law Explained.
This lab supports NGSS 4-PS3-2 (energy transferred by electric currents) and MS-PS1-2 (evidence of a chemical reaction). Download the printable lab above, or find more lessons on our education page.
Watch: the Squishy Battery
Battery questions
How does a battery work in simple terms?
A battery holds two different materials in a chemical paste or liquid. A reaction makes one side release electrons. The electrons travel through your circuit to the other side, and that moving charge is electricity.
What are the three main parts of a battery?
The negative electrode (anode), the positive electrode (cathode) and the electrolyte between them. A separator keeps the two electrodes from touching.
Why do batteries die?
The chemical reaction inside slowly uses up the materials. When they run out, the reaction stops and the battery can no longer push electricity. Rechargeable batteries reverse the reaction when they are charged.
Can you make a battery out of play dough?
Yes. A galvanized (zinc-coated) nail and a piece of copper wire in salty play dough make about 0.8 volts. Six cells joined in a row made about 4.7 volts in our tests, enough to dimly light a red LED.
Is a Squishy Battery like a lemon battery?
Yes, it works the same way. In a lemon battery, the lemon juice is the electrolyte. In a Squishy Battery, the salty dough is the electrolyte. Both use two different metals, usually zinc and copper.
Why does a bigger battery have the same voltage?
Voltage depends on the materials inside, not the size. AAA, AA, C and D batteries are all 1.5 volts. Bigger batteries hold more chemicals, so they can supply more current and last longer.
Printable lab: Squishy Battery (PDF)