Battery Replacement or Upgrade Estimator
Updated .
This estimator compares a battery replacement against a new iPhone on the only basis that makes them comparable: cost per year of remaining use. It uses your battery health, your phone’s age, how many hours you actually need, and the two prices in your own currency. It is a decision aid, not a valuation — enter real quotes rather than list prices.
How it works
The comparison rests on one idea: a battery replacement and a new phone buy different amounts of time, so comparing their prices directly is meaningless. Dividing each by the years of use it delivers makes them commensurable.
The estimator applies these rules:
- Health above 85% — a replacement is not the answer, because the battery is not the constraint. If the phone still falls short, the cause is background activity or a weak signal, and the tool says so rather than recommending a purchase.
- Health below 80% — a replacement is assumed to buy about two further years of ordinary use, so its cost per year is the price divided by two. Between 80% and 85% the assumption drops to about eighteen months.
- A new phone is amortised over five years, which is a realistic full lifespan. Keeping a phone for less makes the new phone worse per year, not better.
- Age of six years or more overrides the arithmetic, because software support rather than the battery becomes the limit, and no repair resets that clock.
The daily shortfall is simply the hours you need minus the hours you get. It exists so the tool does not recommend spending money on a phone that already covers your day.
Worked example
A four-year-old iPhone. Battery health 76%. The owner needs 14 hours and gets about 10, so the shortfall is 4 hours — real, not imagined. A local replacement is quoted at 89, and the phone they would buy costs 829.
Replacement: 89 divided by 2 years is about 44.50 per year. New phone: 829 divided by 5 years is about 165.80 per year. The replacement is roughly a quarter of the cost per year of use, so the verdict is to replace the battery.
Change one input and the answer flips. At seven years old with the same battery health, the age rule takes over: software support is the binding constraint, a replacement buys months rather than years, and the tool reports that replacement is a stopgap. Change a different input instead — health at 91% with the same 4-hour shortfall — and the verdict becomes to fix drain before spending anything, because at that capacity the battery is not what is short.
Frequently asked questions
Why does the tool assume a battery replacement buys two years?
Because a replacement restores full capacity on hardware that is otherwise working, and two further years of ordinary use is a conservative expectation for a phone that still receives iOS updates. Between 80% and 85% health the assumption drops, because less is being recovered.
Why is a new phone amortised over five years?
Because most iPhones remain fully usable for five to six years. If you replace phones more often than that, the per-year cost of the new phone is higher than the tool shows, which strengthens the case for a replacement.
What if my battery health is above 85% but the phone still dies early?
The battery is not the constraint at that level, so a replacement would buy back very little. The cause is usually a background app, background location, or a weak cellular signal.
Does the tool account for the resale value of my old phone?
No, deliberately, to keep the inputs to things you can look up in under a minute. If you would sell the old phone, subtract what you would realistically get from the new phone's cost before entering it.
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