Overview - ISO 12819:2009 (battery life of a battery-powered watch)
ISO 12819:2009 specifies standardized methods to evaluate and label the battery life of battery-powered watches. The standard defines two calculable types of battery life - practical battery life (AP) and theoretical battery life (AT) - and prescribes the parameters, equations and labelling wording manufacturers or distributors must use to inform users. ISO 12819:2009 addresses measurement conditions, self-discharge effects, additional functions and environmental conditions relevant to watch battery life claims.
Key topics and technical requirements
- Two battery-life definitions
- Theoretical battery life (AT): assumes an ideal battery with no self-discharge. Calculated using an equation based on battery capacity and mean current consumption.
- Practical battery life (AP): accounts for self-discharge during storage and use. Two methods are given:
- Method I: linear decrease of capacity.
- Method II: self-discharge proportional to remaining capacity (exponential model).
- Essential parameters
- Battery capacity (C) in mAh (per IEC 60086-3).
- Mean current consumed (Im) by the movement (µA).
- Self-discharge currents: storage self-discharge (Ias) and in-use self-discharge (Iad), with calculation rules and default factors when manufacturer data is unavailable.
- Additional-function consumption (If): daily-averaged current from alarms, lighting, chronographs, etc. ISO provides example daily-use times (Annex A) for common functions.
- Storage time (n) - e.g., manufacturers commonly use n = 0.5 or 1 year for comparisons.
- Default values and factors
- DC (annual capacity loss) defaults: 0.05·C for silver‑oxide cells and 0.02·C for lithium cells.
- K factor for in-use self-discharge: 1 for stored/unworn (
