# Quartz Battery Health Checker - How long will your watch battery last?
1.0-2.5 µA Typical 3-hand draw
18-55 mAh Common cell capacity
2.5-4.5 yr Usual battery life
# How quartz battery life is calculated - the math behind the estimate
Battery life follows a simple electrical formula: Life (hours) = (Cell capacity in mAh × 1000) ÷ Current consumption in µA. Dividing that result by 24 gives you days, and by 365.25 gives you years. For example, a standard SR920SW (371) cell with 40 mAh powering a movement that draws 1.5 µA will theoretically last around 3 years. Reduce the consumption to 1.0 µA and the same cell stretches past 4.5 years. Increase it to 2.5 µA and the battery life drops to under 2 years. Every fraction of a microampere matters when you are planning your service intervals.# Most common quartz watch battery types and their capacities
| Cell Reference | Common Code | Capacity | Typical Use |
|---|---|---|---|
| SR621SW | 364 | 18 mAh | Thin dress watches |
| SR626SW | 377 | 27 mAh | Mid-size quartz models |
| SR920SW | 371 | 40 mAh | Chronographs & multifunction |
| SR936SW | 394 | 55 mAh | Large analog-digital hybrids |
| CR2025 | - | 165 mAh | High-drain LED modules |
Match the original specification
Selecting the wrong cell type can reduce battery life by up to 40 %. Always cross-reference the original battery reference number before installing a replacement. The numerical code tells you the dimensions - for example, SR936SW is 9.5 mm in diameter and 3.6 mm thick.# Why you should always use official caliber consumption values
Movement manufacturers like ETA, Ronda, Miyota, Seiko, and ISA publish official technical datasheets for every caliber they produce. These datasheets list the average current consumption under controlled temperature (usually 22 °C) and with a standard hand torque load. Using a guessed value of 1.0 µA when your movement actually draws 2.5 µA can overestimate battery life by more than 100 %. Always download the official PDF from the manufacturer website or check the caliber reference on specialised databases to obtain the real consumption figure.Battery leakage can destroy your watch movement
An exhausted silver-oxide battery can leak potassium hydroxide, which corrodes the contact springs, the circuit board traces, and even the stepper motor coil. If the tool estimates less than 6 months of remaining life, schedule a battery change during your next routine check. Pay special attention to vintage quartz watches from the 1970s and 1980s - their original batteries are far more prone to leakage after decades inside the case.
# Factors that reduce real-world battery life vs the theoretical estimate
- Temperature extremes - a watch left on a sunny dashboard can see 30 % higher current draw
- End-of-life detection circuits - the two-second tick indicator consumes extra power once activated
- Chronograph or alarm usage - momentary current spikes that add up over time
- Mechanical friction - aged or dirty gear trains increase the torque the stepper motor needs
- Magnetic fields - exposure increases motor torque requirements, draining the cell faster
# How to find the right battery replacement for your quartz watch
- SR (Silver-Oxide)
- Cells stamped with SR (e.g. SR920SW) provide a stable 1.55 V output throughout their life, keeping the quartz oscillator accurate. This is the standard for quality quartz watches.
- LR (Alkaline)
- Cells stamped with LR (e.g. LR41) have a gradually declining voltage, which can cause the watch to run slow or stop prematurely. Not recommended as a replacement for SR cells.
- CR (Lithium)
- Cells stamped with CR (e.g. CR2025) deliver 3.0 V and are used in high-drain modules with LED backlights, large LCDs, or multiple complications.
- Numerical Code
- The four digits encode physical size: the first two digits are the diameter in millimetres and the last two are the thickness in tenths of a millimetre. SR936SW = Ø9.5 mm × 3.6 mm.
# Standard quartz vs solar vs kinetic - how the technology changes the equation
Standard Quartz
Uses a replaceable silver-oxide or lithium primary cell. Battery life depends purely on capacity vs consumption. This is what this calculator is designed for.
- Replaceable primary cell
- Life = capacity ÷ consumption
- Predictable replacement schedule
- Affordable battery changes
Solar & Kinetic
Solar watches use photovoltaic cells to recharge a lithium-ion accumulator. Kinetic watches use a rotor-driven micro-generator to charge a capacitor.
- Rechargeable energy storage
- Life depends on charge cycles
- Capacitor degradation over time
- Not compatible with this calculator
Replace proactively, not reactively
When you see the second hand jumping in 2-second or 4-second intervals, the movement has entered power-saving mode due to low voltage. The battery has approximately 2 to 4 weeks of remaining life. Replace it immediately to avoid leakage damage.Key takeaways for quartz watch battery health
Use the official caliber consumption value from the manufacturer datasheet - a guessed value can overestimate life by over 100 %
Match the original cell type exactly: SR, LR, and CR chemistries are not interchangeable
Replace the battery when the tool shows less than 6 months of remaining life to prevent leakage
Real-world battery life is typically 10-20 % shorter than the theoretical ideal due to temperature, friction, and usage
This calculator is designed for standard quartz movements with replaceable primary cells - not for solar or kinetic watches