20000 mAh at 20 W — 4 h 7 min

Steps this charger can offer

USB PD does not use arbitrary voltages; it picks one of the fixed steps. At the same wattage a higher voltage means a lower current, and any step above 3 A needs a chipped cable.

• 5 V4 ANeeds a chipped cable
• 9 V2.22 AAny cable will do
• 12 V1.67 AAny cable will do
• 15 V1.33 AAny cable will do
• 20 V1 AAny cable will do
• 28 V0.71 AAny cable will do

The line for carrying it on board

Under 100 Wh you simply carry it on. Up to 160 Wh you may bring two with the airline’s approval. Above that it does not fly on passenger aircraft. The reason 26,800 mAh power banks are everywhere: times 3.7 V that is 99.16 Wh, right under the line.

What a power bank really moves

A 10,000 mAh power bank will not fill a 5000 mAh phone twice. What is inside is measured at 3.7 V while what leaves is 5 V, so it shrinks by that ratio and leaks more as heat on the way up. About 6660 mAh actually moves.

Nearby cells

Same battery, other chargers

Same charger, other batteries

How to read this

• These times assume the charger holds its output from start to finish. In practice everything slows noticeably past 80%.
• Multiply mAh by 3.7 V to get Wh. Without a voltage you cannot compare two different batteries at all.
• About 90% of what the charger delivers ends up in the battery — the rest becomes heat.
• Above 60 W the cable needs a chip inside. Twenty volts at 3 A is where a plain cable stops.