🔋 Battery Life Calculator

Why use efficiency factor?

Voltage regulators waste energy. An LDO from 9V to 3.3V operates at only ~37% efficiency — most energy becomes heat. Buck converters are 85–95% efficient. The efficiency factor adjusts effective capacity accordingly.

Sleep mode matters

• An ESP32 active draws ~80–240 mA → weeks on 18650
• ESP32 deep sleep → ~10 µA → months or years on 18650
• Wake every 60s for 100ms: avg ≈ 0.013 mA — huge difference
• Use the Active + Sleep mode tab to model this

Real-world derating

• Cold temperatures reduce effective capacity (Li-Ion -20% at 0 °C)
• High discharge rates reduce capacity (Peukert effect)
• Battery aging: expect 20–30% capacity loss over 2–3 years
• Multiply result by 0.7–0.8 for a conservative estimate

Cut-off voltage & Depth of Discharge (DoD)

Every battery chemistry has a minimum safe discharge voltage. Going below it causes irreversible capacity loss or cell failure — even a single deep discharge can render a Li-Ion/LiPo unusable.

• Li-Ion / Li-Po: cut-off 3.0–3.2 V/cell → use max 80% of rated capacity (some BMS protect at 2.5 V but capacity below 3.0 V is negligible and damages cycle life)
• Lead-acid (SLA/AGM): max 50% DoD for long cycle life; 80% DoD possible but shortens lifespan significantly
• NiMH / NiCd: cut-off ~1.0 V/cell → ~80% usable capacity
• Alkaline (primary): can discharge to ~0.8 V/cell → ~90% usable for most devices
• CR2032 / primary Li (Li/MnO₂): ~2.0 V cut-off → ~90% usable, self-discharge limits shelf life more than DoD

Formula

t = (C × η) / I

where:
t = runtime [hours]
C = capacity [mAh]
η = efficiency factor
I = average current [mA]

For sleep cycles:
I_avg = (I_act × T_act + I_slp × T_slp) / (T_act + T_slp)