The four specs that matter
Wh capacity (the honest size — mAh × 3.7 ÷ 1000), PD output wattage (what it can charge — the laptop gate), input wattage (how fast IT recharges — the travel-day spec), and pass-through (whether it can do both at once). Four numbers, printed small, predicting everything.
Why Wh beats mAh on labels
mAh is voltage-specific (3.7 V cells) — comparing banks by mAh is fair only bank-to-bank. Wh is universal: it compares banks to laptops, phones, and airline limits (100 Wh carry-on cap) on one scale. When two banks claim 20,000 vs 18,000 mAh, the Wh line reveals which is honest.
The airline card
Carry-on only, 100 Wh without approval, 100–160 Wh with (max two), 160+ prohibited. Screenshot the Wh spec before flying; cheap banks omit it and security can refuse them. The calculator's airline line computes Wh from mAh automatically — the number to have ready at the checkpoint.