How the calculation works
Price per 100 Wh = price ÷ (Wh of one unit × units) × 100, with Wh = mAh × 3.7 ÷ 1,000
A worked example
A 20,000 mAh power bank at $25.99 holds 74 Wh: $35.12 per 100 Wh. A 10,000 mAh bank at $15.99 holds 37 Wh and costs $43.22 per 100 Wh, so the bigger bank is the cheaper energy.
Why price per Wh
A power bank's job is to store energy, and watt-hours measure energy. Prices per mAh mislead when labels mix voltages, and prices per unit ignore that a 20,000 mAh bank holds twice what a 10,000 mAh one does. Per 100 Wh, a small bank, a laptop bank and a power station sit on one scale, though each is compared with its own kind in the catalog.
Use the headline mAh
Labels often print two capacities: the headline figure at the cells' 3.7 V and a smaller rated capacity at 5 V, after conversion losses. Use the headline figure for every product you compare, so they are all measured the same way. A power station's Wh is its stated energy.
Common questions
Is a lower price per Wh always better?
For the energy, yes, but output matters too: a laptop needs 65 W or more, and a power station's AC output decides what it can run. Compare price per Wh within the kind of power bank you need.
Why are power stations cheaper per Wh?
Big LiFePO4 batteries cost less per watt-hour than small, light power banks with dense cells and compact electronics. They also weigh far more and cannot fly.
Method: arithmetic from the label values you enter. Reviewed .