# Batteries for small devices

Coin cells, Li-ion and LiFePO4: their voltages, their capacity, and when the capacity on the label actually holds.

Page: https://dharanova.com/learn/batteries · Track: Power · Level: Foundation · Facts last checked 6 October 2026

Read first: [Writing a power budget](https://dharanova.com/learn/power-budget.md)

Diagram: Bar chart of nominal voltage from 0 V: CR2032 3 V, lithium-ion and lithium-polymer 3.6–3.7 V, LiFePO4 about 3.2 V. Beside it, a lithium-ion charge, not to scale: constant current while the voltage rises to about 4.2 V, then constant voltage while the current falls. A CR2032 gives roughly 220–240 mAh only at very low drain; LiFePO4 has less energy per kilogram but longer cycle life and better thermal stability. Do not charge lithium-ion below 0 °C at normal rates: lithium plating damages the anode, so many charger chips read a pack thermistor and pause outside a set range.

## Key points

1. A CR2032 lithium coin cell is nominally 3 V with a rated capacity of roughly 220–240 mAh, but only at very low drain; high pulse currents reduce the capacity you can actually use. [1][2][3]
2. Most lithium-ion and lithium-polymer cells have a nominal voltage of 3.6–3.7 V and are charged to about 4.2 V using a constant-current then constant-voltage profile. [4]
3. Lithium iron phosphate (LiFePO4) cells have a lower nominal voltage of about 3.2 V and less energy per kilogram than other lithium-ion chemistries, but longer cycle life and better thermal stability. [5]
4. Lithium-ion cells must not be charged below freezing (0 °C) at normal rates, because lithium plating on the anode causes permanent damage. Many charger chips read a thermistor in the battery pack and pause charging outside a set temperature range. [6][7]

## Sources

1. [CR2032 product datasheet](https://data.energizer.com/pdfs/cr2032.pdf), Energizer
2. [Lithium Coin Handbook and Application Manual](https://data.energizer.com/pdfs/lithiumcoin_appman.pdf), Energizer
3. [Coin Cells and Peak Current Draw (SWRA349)](https://www.ti.com/lit/wp/swra349/swra349.pdf), Texas Instruments
4. [BU-409: Charging Lithium-ion](https://batteryuniversity.com/article/bu-409-charging-lithium-ion), Battery University (Cadex)
5. [BU-205: Types of Lithium-ion](https://batteryuniversity.com/article/bu-205-types-of-lithium-ion), Battery University (Cadex)
6. [BU-410: Charging at High and Low Temperatures](https://batteryuniversity.com/article/bu-410-charging-at-high-and-low-temperatures), Battery University (Cadex)
7. [BQ2407x USB-friendly Li-ion charger datasheet (SLUS810N)](https://www.ti.com/lit/ds/symlink/bq24074.pdf), Texas Instruments