Estimate how long your battery will last based on capacity (mAh), average current draw, voltage, and real-world efficiency.
Calculate Runtime
Enter battery capacity, current draw and optional parameters.
V
85%
10% (poor)70% (typical)100% (ideal)
Usable capacity (after efficiency/DoD)
Typical Battery Capacities
Common battery types and their approximate capacities for reference.
Battery / Device
Capacity
Voltage
Energy (Wh)
Typical Use
AAA Alkaline
1200 mAh
1.5 V
1.8 Wh
Remote controls, small devices
AA Alkaline
2700 mAh
1.5 V
4.1 Wh
Flashlights, toys, clocks
CR2032 Coin Cell
220 mAh
3.0 V
0.66 Wh
Watches, IoT sensors
18650 Li-Ion
3000 mAh
3.7 V
11.1 Wh
Laptops, power banks, EVs
Smartphone (typical)
4500 mAh
3.7 V
16.7 Wh
Mobile phones
9V Block (Alkaline)
550 mAh
9 V
5.0 Wh
Multimeters, alarms
LiPo 500 mAh
500 mAh
3.7 V
1.85 Wh
Drones, RC models
Lead-Acid 7 Ah
7000 mAh
12 V
84 Wh
UPS, alarm systems
Worked Examples
1Arduino + sensor node
Battery2× AA = 3000 mAh
Current draw15 mA average
Efficiency80%
Runtime≈ 160 h (6.7 days)
2ESP32 IoT device
Battery18650 — 3000 mAh
Current draw80 mA average
Efficiency85%
Runtime≈ 31.9 h
3LED torch
Battery3× AAA = 1200 mAh
LED current300 mA
Efficiency90%
Runtime≈ 3.6 h
4Deep-sleep sensor
BatteryCR2032 — 220 mAh
Avg current5 µA
Efficiency90%
Runtime≈ 5 years
Frequently Asked Questions
How do I calculate battery life? ▾
Battery life (h) = Capacity (mAh) ÷ Current (mA) × efficiency. For a 2000 mAh battery drawing 100 mA at 85% efficiency: 2000 ÷ 100 × 0.85 = 17 hours.
What does mAh mean? ▾
mAh (milliampere-hours) is a unit of electric charge. A 2000 mAh battery can supply 2000 mA for 1 hour, 1000 mA for 2 hours, or 100 mA for 20 hours. To convert to Wh: Wh = mAh × V ÷ 1000.
What efficiency factor should I use? ▾
Use 85–90% for simple direct battery connections. Use 70–80% for systems with a DC-DC converter or boost regulator. Use 50–65% for Li-ion cells in applications where you want to preserve longevity (20–80% DoD).
How do I convert mAh to Wh? ▾
Wh = mAh × V ÷ 1000. A 3000 mAh Li-ion cell at 3.7 V = 11.1 Wh. Airlines use Wh to determine if a battery is allowed as carry-on (limit is typically 100 Wh).
Why is actual battery life shorter than the rated mAh? ▾
Several factors reduce real runtime: voltage sag under load, temperature (cold reduces capacity), aging, DC-DC converter losses, and the fact that batteries cannot be fully depleted. Always apply a 0.7–0.85 efficiency factor for practical estimates.