Homemade batteries
Make a battery by Joe Miller
Ten batteries you can build from fruit, coins, salt water, mud and the ground itself, and everything you need to know about the batteries you already own: which kind to buy, how to make them last, and which ones can hurt you.
Safety first. Homemade cells are low-voltage and low-risk, but wear safety glasses, wash your hands, keep chemicals and small parts away from children and pets, and never eat the fruit or vegetables you used. Never try to build or rebuild lithium or lead-acid batteries at home, and never try to recharge a battery that isn't made to be recharged.
How a battery works How every battery works LOAD ← electrons flow through the wire + + + ions move through the liquid Negative electrode (anode) The "fuel" metal, like zinc. It slowly dissolves and gives up electrons. Electrolyte Salt water, acid, juice or paste that lets ions move between the electrodes. Positive electrode (cathode) Copper, carbon or air. It takes in the electrons that flowed through the wire. Voltage Set by which two materials you pair. Size sets how long it lasts and how much current. Two different metals in an electrolyte make a cell. Wire cells together to make a battery. Every battery, from a lemon to a Tesla pack, has these same parts. Ten batteries you can make Ten batteries you can make, from easiest to most involved Battery Volts per cell Current Effort 1 Lemon 0.9 V 2 Potato 0.8 V 3 Coin stack 0.7 V/pair 4 Salt-water jar 0.9 V 5 Aluminum-air 1.0 V 6 Earth battery 0.6 V 7 Vinegar jar 0.5 V 8 Daniell cell 1.1 V 9 Magnesium cell 1.5 V 10 Mud (microbial) 0.4 V Current bars: more bars, more power. Effort dots: more dots, more materials or care needed. From a 15-minute lemon to a living mud battery. 1. Lemon battery 0.9 V · Easy, 15 minutes
2. Potato battery 0.8 to 0.9 V · Easy, 15 minutes
3. Coin stack (voltaic pile) about 0.7 V per coin pair · Easy, 30 minutes
4. Salt-water jar cell 0.9 to 1.0 V · Easy, 20 minutes
5. Aluminum-air cell about 1.0 V · Medium, 30 minutes
6. Earth battery 0.5 to 0.9 V · Medium, an afternoon
7. Vinegar jar ("Baghdad battery") about 0.5 V (iron) or 0.9 V (zinc) · Easy, 20 minutes
8. Daniell cell (gravity cell) 1.1 V, steady · Harder: uses a poisonous chemical
9. Magnesium salt-water cell 1.4 to 1.6 V · Medium, 20 minutes
10. Mud battery (microbial fuel cell) 0.3 to 0.7 V · Easy to build, a few days to start
Getting enough voltage Series adds volts; parallel adds current and life Series: + to − 1 V + 1 V + 1 V + 1 V + 1 V + 1 V = 3 V Same current. Use this to reach an LED's 2 to 3 volts. Parallel: + to +, − to − 1 V + 1 V + 1 V + Still 1 V, three times the current and three times as long at the same load. Homemade cells give about 0.5 to 1.6 volts each and only a few milliamps: plenty for an LED, clock or calculator, not a phone. Wire homemade cells in series to reach the 2 to 3 volts an LED needs. Know your batteries The 5-gallon bucket battery Can it really last 35 years? The math, the upkeep and the catch.
Battery types Alkaline, lithium, NiMH, lead-acid, LiFePO4: what each is for.
Maintenance and storage Make every battery last longer: charging, storage, terminals, water.
Which batteries are dangerous Lithium fires, button cells and children, acid and gas.