200 charge times — 5000 mAh at 20 W takes 62 minutes
A charge time for every meeting of 20 battery sizes and 10 chargers. mAh only becomes energy once you multiply by a voltage, and a charger’s watts are a voltage times a current.
mAh is not energy
mAh only says how many milliamps could flow for an hour; multiply by a voltage and you finally have energy. This page uses 3.7 V, the figure makers themselves use when they print Wh. So 5000 mAh is 18.5 Wh — and two 5000 mAh cells at different voltages hold different amounts.
Same watts, different volts
The watts on a charger are a voltage times a current. Twenty watts at 5 V would be 4 A, past what a plain cable carries, so it runs 9 V at 2.22 A instead. Raising the voltage to lower the current is exactly what USB PD does.
60 W is where cables part ways
A plain cable carries 3 A. Twenty volts — the ceiling of the older standard — times 3 A is 60 W, so above that the cable needs a chip inside to declare it can carry 5 A. When a 65 W charger fails to speed things up, the cable is usually why.
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.
Charger output
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.
- 5Wan old USB charger5V · 1AAny cable will do
- 10W5V · 2AAny cable will do
- 15W5V · 3AAny cable will do
- 18W9V · 2AAny cable will do
- 20Wphone fast charging9V · 2.22AAny cable will do
- 30W12V · 2.5AAny cable will do
- 45W15V · 3AAny cable will do
- 65Wa laptop charger20V · 3.25ANeeds a chipped cable
- 100W20V · 5ANeeds a chipped cable
- 140Wa workstation laptop28V · 5ANeeds a chipped cable
Find it by battery and charger
A charge time for every meeting of 20 battery sizes and 10 chargers. mAh only becomes energy once you multiply by a voltage, and a charger’s watts are a voltage times a current.
1500mAh5.55Wh
2000mAh7.4Wh
2500mAh9.25Wh
3000mAh11.1Wh
3500mAh12.95Wh
4000mAh14.8Wh
4500mAh16.65Wh
5000mAha phone18.5Wh
5500mAh20.35Wh
6000mAh22.2Wh
7000mAh25.9Wh
8000mAh29.6Wh
10000mAha common power bank37Wh
12000mAh44.4Wh
15000mAh55.5Wh
20000mAh74Wh
26800mAhjust under the cabin limit99.16Wh
30000mAh111Wh
40000mAh148Wh
50000mAha laptop power bank185Wh
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.
Frequently asked questions
Q. How long does a 5000 mAh phone take at 20 W?
62 minutes. Dividing 18.5 Wh by 20 W says 55, but a tenth of what the charger delivers leaves as heat.
Q. I plugged in a 65 W charger and nothing got faster.
Usually the cable. Above 60 W the current must pass 3 A, and that requires a chip inside the cable to declare it.
Q. Can a 10,000 mAh power bank fill a 5000 mAh phone twice?
No. Inside is 3.7 V, out is 5 V, so it shrinks by that ratio and loses more as heat while stepping up — about 6660 mAh actually moves.
Q. Can I take a power bank on a plane?
Under 100 Wh, freely. That is why 26,800 mAh is so common: it comes to 99.16 Wh. Up to 160 Wh you may carry two with airline approval.
Q. Why does charging slow down at 80%?
A lithium cell must taper its current as its voltage rises, so the last 20% can take as long as the first 80%. That is why the table lists the 80% time separately.