A 1.2V Iron-Iron Alkaline Cell From Scrounge
This is not a science project. It’s a real, rechargeable, deep-cycle cell you can build from trash. It’s based on the old Edison nickel-iron battery, but simplified to use only iron and rust. No lead, no lithium, no acid.
Nominal voltage is 1.0-1.2V per cell. Put 5 in series for ∼6V, 10 for ∼12V.
Base Concept
1. Anode (-): Clean iron. A plain steel can. When discharging, iron turns to iron hydroxide and releases electrons.
2. Cathode (+): Rusted iron. Steel wool that you let rust, then packed tight.
3. Electrolyte: Alkaline water that carries ions between them. The electrolyte does not get consumed.
You are just shuttling oxygen between two pieces of steel in different oxidation states.
1. The Anode – The Outer Can
Best option is a standard 15oz steel vegetable can. This is your negative terminal. The can itself IS the battery case and the anode.
Most food cans today have a thin plastic liner inside to prevent corrosion. You must remove it. Easiest scrounge method: hit the inside with a propane torch or throw it in a campfire for 2-3 minutes until the liner smokes and burns off. Then quench in water and hit it quickly with sandpaper or steel wool to expose bare shiny steel. An unlined can is what you want.
Options: any steel can, steel box, steel pipe, or even an old ammo can. Avoid aluminum.
2. The Cathode – The Inner Can
This is where your capacity comes from. You need fluffy iron with a ton of surface area, all rusty.
Take cheap steel wool, #0000 or #0. Wet it with salt water, leave it outside for 2-3 days until it is fully orange/brown and crumbly. That’s your active material.
You need to hold it and make electrical contact:
Scrounge Gold: Tomato paste can (5.5oz) perforated. Drill or punch with a nail 30-40 tiny holes all over it. Stuff the rusty wool in as TIGHT as you possibly can with a stick. The can itself is your current collector (-) just clip your (+) wire directly to the lip. No internal wire needed. This is the cleanest version.
Upgraded: Steel pipe or EMT conduit with holes drilled, stuffed with rust. Will last for years. If you use copper pipe for the inner, the pipe itself is your + lead.
Loose wool = high resistance and low capacity. Pack it like you’re packing black powder.
3. The Separator – Tyvek
You must keep the two cans from touching or you get a dead short. You need a material that lets alkaline water through but stops electrons.
Best to worst:
– Tyvek (house wrap / FedEx / USPS envelopes): Perfect. Porous HDPE that KOH can’t dissolve. One layer is enough.
– Non-woven reusable grocery bag, landscape fabric: Works long term.
– Cotton t-shirt, felt, paper towel: Works for weeks but KOH rots it. Good for testing only.
– Avoid: Plastic bags or plastic wrap – they block ions, battery won’t work.
The separator may be right against both cans. No gap needed. Tighter is better.
Wrap the inner tomato can like a burrito with Tyvek, tuck the bottom, tie with string or zip tie. With grid: seal with a clothes iron on low or hair straightener for 3 seconds. Grid-down: heat a butter knife with a lighter and use it like an iron.
4. The Electrolyte
Best: Potassium hydroxide (KOH), 20-30% by weight in water. That’s about 2-3 cups of KOH flakes per liter of water. KOH gives best performance. Sold as soapmaking lye.
Second: Sodium hydroxide (NaOH), same mix ratio. Works, but self-discharges faster. Sold as 100% lye drain cleaner. Make sure label says 100% lye.
Grid-down: Wood ash lye. Boil hardwood ash in water, filter clear liquid. Weak, but functional at about 30% of KOH capacity. Boil it down to concentrate it.
Mix with distilled water if you have it. Always add lye TO water, never reverse. Wear glasses and gloves – it will burn skin and eyes.
How Much Power?
This size cell – 15oz outer, 5.5oz inner stuffed with ∼50-80g of rusted wool – will realistically give you *3 to 8 Amp-hours at ∼1V.* That’s 3 to 8 watt-hours per can.
Why the range? It depends entirely on how tight you packed the rust and how well you burned off the liner. A loose pack might give 2 Ah, a hydraulic-pressed pack can exceed 10 Ah.
For context: 10 cells in series (a 12V pack) at 5 Ah each = 50 watt-hours. Enough to run LED lights for a night, charge phones, run a radio. Need more? Add more cans in parallel, or use bigger cans – a #10 food service can easily stores 20-30 Ah.
Assembly and Use
1. Burn liner off outer can, sand inside.
2. Perforate inner can, pack tight with rusty wool.
3. Wrap inner can tightly with one layer Tyvek. Tie.
4. Place a plastic bottle cap in bottom of outer can as a standoff.
5. Drop wrapped inner can into outer. Wedge so it can’t rattle.
6. Attach wires – one to outer can (-), one to inner can lip (+).
7. Pour electrolyte until Tyvek is saturated and level is just below top of inner can.
8. Optional but highly recommended – Mineral oil seal:
After you pour the electrolyte, add about 1/8″ (2-3mm) layer of mineral oil, baby oil, or even clean cooking oil on top of the electrolyte in both cans. It will float.
It does two critical things: stops water from evaporating, and stops CO2 from the air getting into the KOH and turning it into potassium carbonate (which kills performance).
Your cell will hold charge way longer and you won’t have to top up water every week. Leave the oil in – ions move under it, it just sits on top as a lid.
You will read 0.8V to 1.2V immediately.
Charging:
Charge at 1.6V to 1.9V per cell. For charging speed: if your cell is 5 Ah, charge at 0.5 amps for 10 hours. That’s what C/10 means – capacity divided by 10. For a 5 Ah cell, C/10 = 5 / 10 = 0.5A. A small 10W solar panel can do this. Do not charge above 1.9V.
You can discharge down to 0.6V. Overcharge just makes hydrogen and uses water – top up with a little water if needed.
Two cans, some rust, and an envelope.