Phones, apps & storage
Phone Battery Life Calculator
A milliamp-hour figure tells you nothing on its own — what matters is the draw of what you are doing. This converts capacity into hours per activity, works out charging time from your charger, and projects how much of that capacity is left after a few years of cycles.
mAh is not a battery-life number
Milliamp-hours measure charge, not energy, and comparing them across devices only works
at the same voltage. Watt-hours are the honest unit:
Wh = mAh × V ÷ 1000. A 5,000 mAh phone cell at 3.85 V holds
19.25 Wh. That is the number to compare against a laptop or a power
bank, and it is why a "20,000 mAh" power bank does not charge a 5,000 mAh phone four
times — the bank's cells sit at a lower voltage and conversion loses 10–20%.
Why fast charging is not linear
A 30 W charger does not fill a battery twice as fast as a 15 W one. Charging runs at near-full power to about 60% of capacity, then tapers steeply to protect the cell, and the last 20% is deliberately slow. A phone that reaches 60% in twenty minutes commonly needs another forty for the rest. The advertised "0–50% in 15 minutes" claims are measuring the easy part on purpose.
How batteries age
Lithium cells lose capacity with charge cycles and with heat. A rough guide is 20% capacity lost after 500 full cycles — for most people that is eighteen months to two years. Two habits accelerate it sharply: charging to 100% and leaving it there, and letting the phone get hot while charging. Both are avoidable, and the modern optimised-charging features that hold at 80% overnight exist precisely because the difference is large.
- Heat is worse than cycles. A phone left on a car dashboard in summer ages more in a day than a month of ordinary charging.
- Partial charges are fine. A cycle is a cumulative 100% of capacity, not a plug-in event. Topping up from 60% to 80% five times is one cycle.
- Deep discharges are avoidable. Repeatedly running to 0% stresses the cell more than any charging habit.
Questions people ask about this
How long does a 5000mAh battery last?
Between about 5 hours of gaming and 30 hours of music playback, depending entirely on what the phone is doing. A 5,000 mAh cell at 3.85 V holds 19.25 Wh; video streaming draws roughly 2.5 W, gaming 4 W or more, and audio playback under 1 W. Mixed everyday use typically lands between 6 and 9 hours of screen-on time.
How do I convert mAh to watt-hours?
Multiply mAh by the nominal voltage and divide by 1,000. A 5,000 mAh cell at 3.85 V is 19.25 Wh. Watt-hours are the only fair way to compare batteries at different voltages, which is why airlines regulate carry-on batteries in Wh rather than mAh.
Why does the last 20% charge so slowly?
Deliberate cell protection. Lithium batteries take a constant current up to roughly 60–80%, then switch to a constant-voltage phase where current falls steadily to avoid stressing the chemistry. Charging that last stretch at full power would measurably shorten the battery's life, so every phone tapers it.
How long before a phone battery needs replacing?
Most cells reach 80% of original capacity after about 500 full cycles, which is eighteen months to two years of daily charging. Heat accelerates this more than cycle count does. A battery at 80% is still usable; it is when the phone starts shutting down above 20% indicated charge that replacement becomes necessary.
Where these numbers come from
Rates on this page were last checked against the published price lists on . Grading companies change fees and pause tiers without notice — confirm the total on the submission form before you pay.