Battery Self-Discharge

Formula

Description

Batteries lose charge over time even when disconnected, due to internal chemical reactions. The self-discharge rate varies dramatically by chemistry: lithium-ion cells lose 1-5% per month, NiMH batteries 15-30% per month (low-self-discharge NiMH like Eneloop only 1-3%), and lead-acid batteries 3-20% per month. This exponential decay model helps predict shelf life and plan maintenance charging schedules. Temperature significantly affects self-discharge, roughly doubling for every 10°C increase.

Variables

• Crem — Remaining capacity after storage (mAh)
• C0 — Initial capacity (mAh)
• rate — Daily self-discharge rate (decimal)
• days — Number of days in storage

Practical Notes

For monthly rate conversion to daily: daily_rate = 1 - (1 - monthly_rate)^(1/30). Primary (non-rechargeable) lithium batteries have extremely low self-discharge (less than 1% per year), making them ideal for emergency equipment and long-term deployments. Store batteries at 40-60% SOC and cool temperatures for minimum degradation.