An iPhone battery is designed to keep about 80% of its original capacity after 500 complete charge cycles — or 1000 cycles on iPhone 15 and later — and both of those are design targets measured under ideal conditions, not a promise about your phone. Turned into years, that is roughly two to five years of ordinary use. The two things that decide where you land in that range are how hot the battery gets and how much of it you push through every day.
This page is about lifespan — how long the cell itself lasts, and how fast you are spending it. It is not about why the phone dropped 20% overnight, and not about whether the percentage is accurate; calibration and the drain reading are separate questions, linked at the end.
What Apple actually specifies — and what it does not
Apple's own battery documentation is narrower than the internet usually reports. Two statements are the whole factual basis:
- iPhone 14 and earlier: a normal battery is designed to retain up to 80% of its original capacity at 500 complete charge cycles, under normal conditions.
- iPhone 15 and later: designed to retain 80% of capacity at 1000 complete charge cycles, under ideal conditions.
Everything else is inference. Three qualifiers matter:
- It is a design target, not a guarantee. "Under ideal conditions" means a lab cell at a comfortable temperature doing standard charge and discharge. A phone that lives in a hot car or is gamed on while charging is not operating under ideal conditions, and its curve will arrive at 80% sooner.
- It says nothing about years. Apple deliberately avoids a lifespan in years, because years depend entirely on your cycles, your temperature, and plain calendar aging. Any "iPhone batteries last exactly N years" claim is someone else's arithmetic, including the arithmetic below.
- Gradual capacity loss is normal wear, not a defect. Which is why a battery that has faded is a paid service rather than a warranty claim; coverage usually speaks to defects and, in some plans, to a battery that has already fallen below 80%.
Apple also separates two terms that get blurred: battery life is how long one charge runs (hours), and battery lifespan is how long the cell stays useful (years). This page is the second one. If your complaint is the first — a phone that no longer makes it to dinner — read Battery Health Explained to see how the runtime number is measured.
Turning your usage into an estimate
The estimate is four lines of arithmetic, and it is worth doing rather than guessing.
- A cycle is 100% of discharge, not one plug-in. Two days of 50% each, or four days of 25%, add up to one cycle. Partial top-ups are counted in proportion, which is why "I charge it twice a day" is not automatically two cycles.
- Cycles per day = your average daily discharge ÷ 100. A day that burns 60% of the battery is 0.6 cycles.
- Cycles per year = cycles per day × 365.
- Years to 80% ≈ (design cycle budget − cycles already used) ÷ cycles per year. The budget is 1000 on iPhone 15 and later, 500 on iPhone 14 and earlier.
| How you actually use it | Daily discharge | Cycles per day | Years to 80%, 1000-cycle design (iPhone 15+) | Years to 80%, 500-cycle design (iPhone 14 and earlier) |
|---|---|---|---|---|
| Light: messages, email, topped up at a desk | ~30% | 0.3 | ~9 | ~4.5 |
| Typical: mixed use, one charge most days | ~60% | 0.6 | ~4.5 | ~2.3 |
| Heavy: camera, navigation, games — one full charge a day | ~100% | 1.0 | ~2.7 | ~1.4 |
| Very heavy: two charges a day, hotspot or long gaming sessions | ~150% | 1.5 | ~1.8 | ~0.9 |
To get your own number rather than the table's, use the counter iOS already keeps. On iPhone 15 and later, Settings → Battery → Battery Health & Charging shows Cycle Count. Note it today, note it again in 30 days, multiply the difference by 12, and you have your real cycles per year — no estimation of screen-on time required. On earlier models there is no cycle counter, so estimate from how much of a charge a normal day consumes.
Two honest warnings about the table. First, capacity fade is not a straight line: it tends to move faster in the first months, flatten through the middle, and then accelerate again late in life, so the table tells you roughly which year matters, not which month. Second, the table only counts cycles. Heat, time at full charge, and calendar aging are layered on top of it, so treat every figure in it as a best case.
What actually accelerates aging, by weight
Batteries do not wear out from one villain. They wear out from four, and they are not equally important.
① Heat — the largest and most permanent factor. High temperature speeds up every chemical reaction inside the cell, including the unwanted ones; a widely used rule of thumb is that reaction rates roughly double for every 10°C. A summer dashboard, a phone charging under a pillow, gaming in a case on a bed, or a hot car left in the sun all cost real, unrecoverable capacity. If you change one habit after reading this page, change this one — see Why Your Phone Gets Hot for where the heat actually comes from.
② Hours spent at or near 100% — second, and the one most people can fix in Settings. A full cell sits at its highest voltage, and voltage stress ages the chemistry whether or not current is flowing. The cost scales with hours, not with how many times you reached 100%: a phone that hits full at 2 a.m. and sits on the charger until 8 a.m. has spent six hours in the worst state of charge. Optimized Battery Charging and the charge limit exist to cut exactly that time, and 80% Limit or Full Charge? explains which one fits your day.
③ Deep discharges and time at low voltage — real, but third. The bottom of the range is hard on the cell, and spending the same energy in shallower cycles wears it slightly less than in deep ones. The failure mode to avoid is not "reaching 1%" but parking there: a phone left at 0% for days can fall into a deep-discharge lockout where it refuses to charge at all, which is a repair rather than a reading problem.
④ Fast charging itself — the smallest of the four, when the phone is cool. The mechanism is heat, not wattage. A 20W or 30W charge on a cool, ventilated phone is not meaningfully harder on the cell than a slow overnight charge, while fast charging a phone that is already warm — in a case, in the sun, while gaming — stacks heat and does cost capacity. Untested cheap chargers and cables are a separate, worse problem, because unstable output can misbehave at the circuit level.
One factor outside that list deserves its own line: calendar aging. Lithium-ion cells lose capacity with time even if you never cycle them, which is why a "new in box" two-year-old phone does not have a new battery. Storing a phone at roughly half charge, powered off, in a cool place is the least harmful way to shelve it.
How to tell your battery is near the end of its life
No single reading answers this. The reliable signal is a pattern across three things, and the number is the least important of them.
The trend in Maximum Capacity, not its level. A point or two of movement is noise, and it moves for other reasons too. A steady slide in one direction over a few months is aging. Judge the slope, not the snapshot.
Cycle count against the budget. On iPhone 15 and later, Cycle Count tells you how much of the designed budget you have spent: 700 cycles on a 1000-cycle design means you have used 70% of the cycles that Apple expected to bring the cell to 80%. That is a firmer statement than the health percentage alone.
Behavior that shows the cell, not an app, is the constraint:
- The phone shuts down at 20–30% at room temperature, or the percentage dives and then recovers (25% → 18% under load → 22% once you stop). A worn cell sags under load; a healthy one does not.
Peak Performance Capabilityreports that performance management has been applied, with lag and warmth under light tasks.- Runtime no longer covers your day even though the per-app battery list is clean and the pattern has held for a week. If the drain appeared suddenly, or one app dominates the list, the cell is probably not the cause — check what the per-app list is telling you.
Equally important is what these signals are not. Fast drain on one day, drain in the week after a big update, and a percentage that moved a point are not evidence of a worn battery. Neither is a shutdown in the cold: cold sags the voltage temporarily and warming the phone restores it, which is a temperature effect rather than lifespan (Cold-Weather Battery Behavior explains the difference). The version that counts is the one that happens at room temperature and repeats.
Replace the battery, or replace the phone?
The question is not "is the battery worn" — that is measurable. It is "is the battery the only thing that is worn?" That is a judgment about the whole device, and these are the axes worth putting on paper.
The battery-only case. The phone is still fast, storage has headroom, the screen and camera are fine, and the model still receives iOS updates. Here a battery service is the cheapest way to add years to a device you already own, and it typically costs a small fraction — often in the region of a tenth — of what a comparable new phone costs, though the exact price varies by model and region, so get a local quote. If you expect to keep the phone for another two years once it is repaired, the arithmetic is strongly on replacement.
The several-things case. Battery plus a cracked screen, permanently full storage, a camera you have outgrown, and a model near the end of its OS support. Here the battery is the visible symptom but not the reason the phone feels old, and a new battery buys time rather than solving anything. That does not make it wrong — it is often the right move if you plan to pass the phone on or wait for a model you actually want.
Five questions that make the choice explicit:
- If the battery were new tomorrow, how long would you keep this phone? Two more years means the battery is the fix; "I want a new phone anyway" means the battery was never the decision.
- What else has degraded? Screen, storage, camera, cellular, and the water-resistance seals that age with every repair — list them honestly.
- What is the ratio? Battery service cost divided by new-phone cost. As a rule of thumb, the smaller that fraction, the more a replacement looks like cheap insurance on a healthy device.
- What does your coverage say? Warranty and AppleCare-style plans often state a capacity threshold (commonly below 80%) at which battery service is covered. Confirm your own terms before paying out of pocket.
- Does resale matter? A fresh battery lifts the value of an otherwise good phone if you sell it yourself, while trade-in offers may barely notice.
None of those answers is fixed in advance. A four-year-old phone with 900 cycles, a clean screen and two more years of OS support is a replacement battery. A three-year-old phone with a smashed screen and storage that is full 100% of the time is a new phone with extra steps — and only you can weigh which of those you are holding.