Sleep Current Arithmetic behind a Five Year Battery Claim
Five-year battery claims require balancing microampere sleep floors, primary cell passivation derating, and protocol airtimes across 43,800 hours.
Primary Battery Derating
Meaning
Engineering reduction of the nominal capacity of a non-rechargeable battery accounts for real-world environmental and operational losses during its field service. Applying primary battery derating ensures that a wireless device operates reliably throughout its designed lifetime under varying temperatures and current loads. Designers use specific multipliers to calculate the realistic energy budget rather than relying on the manufacturer’s ideal laboratory specifications.
Temperature Effect
Chemical performance degraded at sub-zero temperatures reduces the available energy due to increased internal resistance. This phenomenon causes the voltage to drop below the minimum shutdown threshold before the cell has released its chemical capacity.
Discharge Profile
Continuous drain and periodic high-current pulses draw energy differently, affecting the overall cell efficiency. When a device requires brief, intense current pulses for long-range radio transmissions, the chemical recovery of the cell is challenged. This condition requires a more conservative correction factor than a system with a continuous, low-power current draw.
Lifetime Calculation
Final capacity estimates incorporate self-discharge rates alongside the active load calculations to determine the end-of-service date. This procedure involves compounding the annual self-discharge percentage over the target operational lifespan. The resulting value represents the true battery capacity available to the system, which determines the maximum allowable interval between transmissions.