Calculate Battery Capacities,
True Charges per Bank.
Free power bank calculators: how many phone charges a bank really holds, recharge times, laptop compatibility, and solar panel pairing.
100 Watt-Hour Airline Limit
TSA / FAA restricts carry-on lithium battery banks to 100Wh (approx 27,000 mAh at 3.7V nominal).
Voltage Boost & Heat Loss
Internal 3.7V cells boost to 5V/9V/20V USB-PD, resulting in 25–30% energy dissipation as heat.
Full Recharges Guaranteed
Divide true usable watt-hours by phone battery capacity to determine real off-grid charges.
PowerBankMath Calculators
Power Bank Charges Calculator
Real charges per power bank — the voltage-conversion and efficiency math the label hides.
Charging Time Calculator
How long the bank (or phone) takes to recharge — by wattage, with the taper-curve honesty.
Laptop Power Bank Calculator
Whether a power bank can run your laptop — wattage gates, Wh capacity, and real runtime added.
Solar Panel Charging Calculator
Solar panel to power bank pairing — real-world wattage, hours of sun, and the recharge forecast.
Technical Reference Guides
Reading a power bank label like an engineer
mAh vs Wh, input vs output, and the four specs that actually predict travel performance.
The taper, the heat, and the truth about fast charging
Why the last 20% takes as long as the first 80, and what actually kills lithium batteries.
12 mistakes people make with power bank capacity
The recurring errors we see in power bank capacity — what causes each one, and the habit that prevents it.