We know that you can start a fire with a battery. the better prepared you are the easier it is going to be.

I am not prepared and all I have in my pockets is my car keys, which includes a keyless entry fob that has a '3v Lithium Coin Cell Battery' is it possible to start a fire with this battery? All I have is the metal key ring, finger nail clippers, and a couple of other keys on the ring.

I don't have a tiny screwdriver to get the battery out, so I am going to have to use a rock to break the key fob. I suspect that banging two rocks together would be a more effective fire starter, but I might be wrong.

Can I start a fire with my key fob battery?


With just the right equipment in a laboratory setting, you can use the energy in a key fob battery to cause a spark. You can then use that to start a fire under the right conditions.

However, that's not going to happen in any realistic back country conditions. The voltage and current capability of a key fob battery are just too low.

The reason you can sometimes use a car battery for starting a fire is because a car battery can deliver a massive amount of current. When shorting the battery with a small wire, the contact point gets so hot that some of the metal is vaporized, causing a spark. Sometimes small amounts of molten metal are also shed off. A key fob battery just doesn't have the oomph to do that.

In addition, it's not easy to start a fire with just a electric spark unless you have ignitable vapor. A few drops of stove fuel on tinder, then letting that vaporize for a few seconds can work, but trying to light solid tinder directly is very difficult. The reason this is sometimes successful with a car battery is due to the molten metal resulting from the high current, not the spark itself. With a car battery, you can even get small wire to glow, and then melt. A key fob battery isn't capable of that.

  • 2
    Steel wool is the easiest way to use a battery to start a fire. Even a PP3 (with a fairly high internal resistance) will get very dry tinder (or liquid fuel) going using steel wool. Now I want to experiment! – Chris H Sep 15 '18 at 14:15
  • 1
    @Chris: Yes, what you really want is very thin wire. Steel wool is a handy way to get such wire. Steel also has the advantage of oxidizing when heated enough. In this case, steel wool isn't available. Although I haven't tried it, I expect a key fob battery to be too week to get steel wool hot enough to start a fire. You need something with decent current capability, like a flashlight battery. – Olin Lathrop Sep 15 '18 at 14:20
  • 1
    Steel's high resistivity compared to electrical wire is also a help. Brass (from the keys) is also a poor conductor but I don't think there's any way to make a filament out of it with the constraints in the question – Chris H Sep 15 '18 at 16:09
  • 1
    electronics.stackexchange.com/questions/234901/… More keyfob battery notes. New battery momentary 0.1amp peak @ 3V so 0.3W and that’s best-case. So you’d better have made some good tinder (with your Survival Nailclipper) – mmcc Sep 16 '18 at 4:53
  • 1
    @mmcc: There is a very big difference in short circuit current and internal resistance between a AAA battery and a coin cell, even a large one like a CR2032. You're just not going to get "steel wool" hot enough to start a fire with just a small coin cell. I'm a electrical engineer, and I could design a circuit that would make a spark powered from only a coin cell. However, the required parts aren't available in the wilderness. Making a spark and heating wire to burning temperature are also two different things. – Olin Lathrop Sep 16 '18 at 13:54

A bit more than a comment on Olin's answer:

I've done an experiment, and no, you can't.

I took:

  • a brand new CR2025
  • some steel wool to make it easier; this is a nice firelighting filament with bigger batteries
  • a tissue

I shorted the cell using the steel wool, held in a pad of tissue to provide tinder and keep the heat in. It got fairly warm for a couple of minutes, even through the tissue, but when it cooled and I opened the tissue it wasn't even blackened. If I couldn't get close with the contents of a house and garage at my disposal, you're not going to be able to do it in the field.

  • Agreed. I tried too (CR2016 and a single strand of fine steel wool) and got nothing. – mmcc Sep 17 '18 at 23:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.