Choosing a battery for your next low power radio project

Just chuck a 2032 coin cell in! (Or should you?)

A large number of small electronic devices (from flickering faux-candle night lights to the keyfob that unlocks your car doors) are powered by the ubiquitous lithium “coin cell”, and while there are other sizes in common use, that usually means a “2032” cell.

So, when you choose a battery for your next low power radio project (maybe a miniature transmitter, or an ultra-low-power sensor node), it's easy to select this same familiar power cell. It’s inexpensive, widely available, with plenty of clips, holders and leaded variants. It even provides a conveniently modern-compatible 3V output.

However — think again.

These lithium manganese dioxide coin cells do have advantages: high stability, long shelf life, decent energy density, and a helpful 3V output (peaking around 3.3V initially). But the big drawback is peak current capability.

Even a larger 2032 cell is typically only rated for a few milliamps. Internal resistance is significant. They work beautifully for memory backup tasks or ultra-low-power CMOS circuitry — but they perform poorly when powering low-power wireless modules.

A Simple Practical Test

A mid-priced 2032 cell (brand “Pifco”), fresh at 3.4V with negligible load:

  • Under a 100Ω load (~30mA), voltage immediately dropped to 3.02V
  • After 1 minute → 2.67V
  • After 5 minutes → 2.56V

Once the load is removed, the voltage recovers, but the cell simply cannot maintain sufficient voltage under realistic radio transmission load. Even though the rated capacity might be ~230mAh, in real wireless usage it behaves as if it has far less usable capacity.

Comparing with Silver Oxide Cells (e.g., SR44)

A pair of SR44 silver oxide cells (160mAh each):

  • Nearly the same initial voltage (~3.2V total)
  • Under the same 30mA load, voltage holds much more steadily
  • Discharge curve is flatter — meaning longer usable runtime
  • Better suited for low-power wireless tasks

Why the 2032 Struggles

The 2032 can deliver its rated capacity only at very low currents (sub-milliamp range). As soon as current demand rises (as in wireless transmitters), internal resistance causes:

  • Voltage collapse
  • Large loss of usable capacity
  • Poor runtime

Other Battery Options

  • Silver Oxide — Very flat discharge curve, good current capability; small sizes only, higher cost.
  • Lithium Manganese (CR series) — Long life, stable, cheap; weak under load.
  • Alkaline — Cheap, high peak current; non-constant voltage, shorter shelf life.
  • Lithium Thionyl Chloride — Excellent capacity and stability; expensive and limited availability.
  • Lithium Ion / Li-Po — High current capability; needs protection and care.

If You Must Use a DC-DC Converter

A DC-DC converter can boost voltage as a battery discharges — but it does not fix poor peak current performance and may introduce RF noise. Layout and filtering become critical in radio designs.

Conclusion — Choosing the Right Cell

There is no one-size-fits-all answer. General guidance:

  • Maximum performance needed? → Lithium Thionyl Chloride
  • Smallest size required? → 2–3 Silver Oxide cells
  • Lowest cost matters? → Multiple Alkaline cells
  • Avoid powering radio transmitters directly from CR2032 whenever possible.

Myk Dormer for Radiometrix Ltd
August 2025

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