Electronic – Coin Cell Battery Safety

batteriesbattery-operated

I'm working on a wearable project that is really space constrained. Originally, I had planned to use a Li-Ion battery, but I opted out of it because the person wearing it won't be able to take the wearable off in case there is a catastrophic battery failure.

I would use a triple-A battery, but those are too large.

What battery can I find that is smaller than a triple-A battery, but still fits the following constraints:

  • Safter than Li-Ion
  • Smaller and lighter than triple-A
  • Nominal voltage of 3.0V (I would be willing to use 2 1.5V cells if they are small enough)
  • Charge capacity >= ~50mAh
  • Capable of delivering up to 300mA in very short bursts for rf transmission (about 30 milliseconds). Otherwise the "resting" current consumption of the system will be on the order of 10μA.

I've found plenty of small batteries that satisfy one or 2 of these requirements above, but I can't seem to find one that fits all 5 except the 110mAh li-ion that I linked above.

Best Answer

I've never heard of a "safe" battery for sale.

  1. Lead acid - Gee, Lead and Sulfuric acid... totally not safe.
  2. Alkaline - not too dangerous to you (read: Less dangerous but still caustic), but when they leak, your electronics are gone.
  3. Nickel Cadmium - Cadmium, that's poisonous if it breaks.
  4. Nickel Metal Hydride - Hydrides are extremely reactive.
  5. Lithium anything - Lithium will literally burst into flames on uncontrolled contact with oxygen. So don't puncture one.

There are a few prototypes for safe batteries going on. Al-ion, nickel film protected Li-ions, etc. But, those aren't available.

Instead, You should make sure that the Li chemistry you're using isn't Li-FePO3 (this one is the most dangerous of the Li-ions), and protect the battery from over-heating by creating a circuit that cuts off current from the battery if the battery becomes too hot. Heat is the most dangerous thing that Li-ions go through, since they are generally very well sealed against outside oxygen getting to the lithium. Also using a standardized connector so that the battery can be replaced after a few years will help give the project some longevity and keep it safer. As batteries age they become more prone to failure, catastrophic or otherwise.

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