Formulas & Calculations
📊 Why Wh is more useful than mAh:
A 10,000 mAh power bank at 3.7V holds 37 Wh. But a "10,000 mAh" label on a 5V USB output only delivers ~6,500 mAh to your phone after voltage conversion losses. Wh gives you the true energy stored regardless of voltage.
Frequently Asked Questions
Why do I need voltage to convert mAh to Wh?
Watt-hours represent total energy stored. Since energy = power × time and power = voltage × current, you need voltage to convert from current-based (mAh) to energy-based (Wh) units. Without voltage, you only know the charge capacity, not the actual energy.
What voltage should I use for lithium-ion batteries?
Use 3.7V for single lithium-ion cells (phones, power banks, drones). Use 3.2V for LiFePO4 cells. Use 12V, 24V, or 48V for solar battery banks. Use 11.1V or 14.8V for multi-cell laptop batteries.
What is the difference between mAh and Wh?
mAh (milliamp-hours) measures electric charge capacity — useful for comparing batteries at the same voltage. Wh (watt-hours) measures actual energy stored — better for comparing batteries at different voltages, like a 3.7V phone battery vs a 12V solar battery.
My power bank says 10,000 mAh but only charges my phone 2–3 times. Why?
Power banks store energy at 3.7V internally but output at 5V USB. This voltage conversion loses about 10–15% of energy. Additionally, your phone battery is typically 3,000–4,000 mAh at 3.7V (~11–15 Wh), so a real 37 Wh power bank realistically delivers 2–3 full charges after losses.
How do I use mAh to Wh conversion for solar battery sizing?
Solar batteries are rated in Ah (amp-hours) at a system voltage (12V, 24V, 48V). Multiply Ah × voltage to get Wh, then by 1,000 to get mAh if needed. For example, a 100Ah 12V battery = 1,200 Wh = 1,200,000 mAh. Our
battery runtime calculator handles full solar storage sizing.