Enter a battery’s mAh, the charger’s output and the starting charge to estimate the charge time — ideal and realistic, with losses included.
How charge time is estimated
The first-order answer is simple division: capacity in mAh over charger output in mA. Reality adds two corrections this calculator is honest about — charging is imperfect (heat and conversion typically cost around 20%), and lithium batteries deliberately slow down for the final stretch to protect the cells. You get the ideal figure and the realistic one, and the note about the taper.
How to use it
- Enter the battery capacity in mAh (phone spec, power bank label).
- Enter the charger’s output in mA (a 10 W/5 V charger ≈ 2000 mA).
- Set the starting percentage and read both estimates.
The formula
A worked example
A 5,000 mAh battery from empty on a 2,000 mA charger: ideally 2 h 30 m, realistically about 3 h 00 m with losses. From 50% it roughly halves. And the everyday observation — phones sprint to 80% then crawl — is the charge controller’s taper, not a fault: the final 20% is deliberately gentle.