Professional scenario conversions
Battery capacity conversion logic
Battery specs mix watt-hours, milliamp-hours, and nominal voltage. Converting between mAh and Wh requires voltage; skipping that step invalidates cross-device comparisons.
Airlines and fire-safety rules cite Wh because it bounds stored energy; mAh without voltage does not.
Key takeaways
- Wh = Ah × V; mAh/1000 → Ah first.
- Compare power banks at similar voltage and conversion efficiency.
- Wireless charging: wall Wh > phone Wh—efficiency matters.
- Aging packs lose mAh—remeasure for year-two comparisons.
How to convert
1 Wh = 3,600 J
Wh is energy
Watt-hours tell you how much energy the pack can deliver at the cell’s typical voltage curve.
mAh is charge
Milliamp-hours are convenient for phones because voltage is similar across models, but laptops need Wh for aviation limits.
Use Wh = Ah × V
Convert mAh to Ah by dividing by 1000, multiply by nominal volts to get Wh; use manufacturer-stated voltage ranges when available.
Regulatory and travel limits
Airlines cite Wh limits for spare lithium packs; mAh-only labels should be converted carefully with printed voltage.
Cycle life vs headline capacity
Older packs lose mAh; comparing Wh after a year needs remeasurement, not brochure numbers.
Wireless charging losses
Qi efficiency varies by coil alignment; Wh drawn from the wall exceeds Wh stored in the phone—compare systems at the same input power.
Series vs parallel packs
mAh adds in parallel at the same voltage; series strings raise voltage—never sum mAh across series without checking the wiring diagram.
USB PD vs proprietary rails
Fast-charge profiles use different V×I ladders; Wh-per-minute comparisons need the negotiated PDO, not the cable label alone.