Phone batteries get weaker over time. That is normal, but the speed of decline depends on heat, charging behaviour, and how the phone is used day to day.
This guide explains what battery health means, why lithium batteries degrade, what fast charging changes and what it does not, and what to expect if you keep a phone for 2 to 4 years.
Battery life matters most on a long contract, so if you are weighing up a 24 or 36 month deal it is worth reading alongside our pay monthly comparison.
Reviewed by Phil Brown, founder of Mobile Phone Finder. Phil has worked in the UK mobile industry, including retail management at Three UK, and has spent over a decade building consumer technology comparison platforms. About the author
What is battery health?
Battery health describes how much capacity your battery can hold compared to when it was new.
If a phone launched with a 5,000 mAh battery and after two years it can effectively hold about 4,000 mAh, its capacity has dropped to roughly 80 per cent. You will notice this as shorter daily battery life.
Capacity is measured against charge cycles rather than calendar time. One cycle is the equivalent of using 100 per cent of the battery, which can be made up of several partial charges. Manufacturers rate batteries by how much capacity remains after a stated number of cycles, and that figure is the most useful single number for judging how a phone will age.
How to check battery health on your phone
On iPhone, go to Settings, then Battery, then Battery Health and Charging. This shows your maximum capacity as a percentage of when the battery was new. Apple recommends considering a battery replacement when capacity drops below 80 per cent. On recent models the same area also shows cycle count and the date the battery was manufactured.
On Samsung, go to Settings, then Battery, then Battery information. This is available on recent Galaxy devices. Some older Samsung models do not surface this natively, and third party apps such as AccuBattery can give an estimate.
On Google Pixel, cycle count appears in Settings, then About phone, then Battery information.
On other Android devices, battery health visibility varies by manufacturer. Some expose it in Settings, then Battery. If your device does not show this information natively, your network or manufacturer support team may be able to help.
Why phone batteries degrade
Most phones use lithium-based batteries, often described as Li-ion or Li-Po. These batteries degrade because of chemical ageing. Even if you do everything right, capacity slowly reduces over time.
The main factors that accelerate wear are:
- Heat, since high temperatures speed up chemical ageing
- High state of charge, since sitting at or near 100 per cent for long periods increases stress
- Deep discharges, since frequent trips to very low percentages can increase wear
- Charge cycles, since cycles accumulate over time even if you top up in small amounts
How many charge cycles a phone battery lasts
Cycle ratings are the closest thing to a like-for-like durability measure, and they have improved considerably.
Apple states that iPhone 15 and later models are designed to retain 80 per cent of original capacity at 1,000 complete charge cycles under ideal conditions. Earlier iPhones were rated to 500 cycles at the same capacity. Recent Google Pixel models are rated to a similar standard, and current Samsung flagships are generally rated at or above it.
At roughly one full cycle a day, 1,000 cycles is about three years of heavy use or closer to five years of average use. That is a useful figure to hold against a 36 month contract, because it tells you whether the handset is designed to still be performing acceptably when the contract ends.
Budget handsets are frequently rated lower, sometimes in the 500 to 800 cycle range, which is one of the less visible differences between a cheap phone and an expensive one.
Fast charging: what it changes
Fast charging is convenient, but it can increase battery wear because it tends to produce more heat and pushes more energy into the battery in a shorter time.
Modern phones manage this with charging curves, temperature monitoring, and sometimes by slowing down charging near 80 to 90 per cent. That helps, but it does not eliminate the trade-off.
Heat is also why phones with stronger build protection and sealing can sometimes retain battery health better over time. If durability matters to you, understanding IP ratings on phones can help explain how devices handle heat, moisture, and long-term exposure.
The practical takeaway is that fast charging is fine to use, but if you keep a phone for several years, reducing heat and avoiding constant high charge will usually help long-term health.
Charging habits that actually help
- Avoid heat. Do not charge under pillows or in direct sunlight.
- Do not leave the phone at 100 per cent for long periods. Enable optimised charging if it is available.
- Topping up is fine. Smaller, frequent charges are generally less stressful than full cycles.
- Use reliable chargers and cables, since poor quality accessories can increase heat.
- Consider a charge limit if your phone offers one. Several manufacturers now let you cap charging at 80 or 85 per cent, which reduces the time the battery spends under the most stress.
You do not need perfect routines. Most gains come from reducing avoidable heat and avoiding leaving the phone fully charged for long stretches every day.
What to expect over time
Battery ageing varies by user, but a realistic expectation for many phones is noticeable decline after 18 to 24 months of regular use.
Heavy use such as gaming, hotspotting, and frequent fast charging can shorten this timeframe. Lighter use and cooler operating conditions can extend it.
This matters more than it used to, because contract lengths have grown. On a 36 month contract you will spend the final year or more of the term on a battery that has measurably declined, and on a 48 month term longer still. That is worth weighing when a longer contract is offered as the cheaper monthly option.
Battery replacement and the 2027 EU rules
Replacing a battery is usually far cheaper than replacing a phone, and it is the single most effective way to extend the usable life of a handset you otherwise like.
Costs vary by manufacturer and model, and an out of warranty replacement is normally a fixed service charge rather than a repair quote. It is worth checking that figure before assuming a phone with a tired battery needs replacing.
The rules are also changing. Under EU Regulation 2023/1542, from 18 February 2027 portable devices placed on the EU market must have batteries that users can replace themselves. There is a significant exemption: if a battery retains 83 per cent of capacity after 500 cycles and 80 per cent after 1,000 cycles, and the device carries an IP67 rating or higher, the battery does not need to be user replaceable and replacement can be restricted to professional repairers.
In practice that means most flagships are expected to qualify for the exemption and keep sealed batteries, while cheaper handsets that do not meet the cycle threshold will need to change. The regulation is not retroactive and applies to new models placed on the market after that date. It also introduces a digital battery passport, accessible by QR code, covering information including the battery's state of health.
The rules apply to the EU rather than the UK, but manufacturers rarely design separate hardware for one market, so the practical effect on what is sold here is likely to be similar.
If repairability is a priority now rather than in 2027, some manufacturers already design for it. Our HMD page covers the clearest current example.
Battery health when buying refurbished
A refurbished handset is partway through its battery life before you start, which is the specification that most affects how it performs day to day.
Ask three questions before buying. What battery health percentage the device is supplied at, since some sellers state a minimum and others do not. Whether the battery has been replaced as part of the refurbishment. And what warranty applies, and whether it covers the battery specifically.
A refurbished phone at 85 per cent capacity is not a problem in itself, but it is not equivalent to a new one, and the price should reflect that. Our Mozillion page covers certified refurbished stock in more detail.
Common battery myths
- Closing apps saves battery health. Usually not. Modern operating systems manage background apps efficiently.
- Fast charging ruins batteries instantly. Not instantly, but heat can accelerate wear over time.
- You must fully drain the battery to calibrate it. Generally unnecessary, and it can add wear.
- All mAh numbers are directly comparable. Efficiency also depends on the chipset, screen, and software.
- Charging overnight is always harmful. Most phones now manage the final stage of charging to reduce time spent at full charge.
How to assess battery health when choosing a phone
If you plan to keep your phone for more than three years, consider the following factors:
- Cycle rating, which is the closest thing to a comparable durability figure
- Battery capacity and efficiency, since it is not just about mAh
- Charging controls, such as optimised charging and charge limit modes
- Thermal management, since devices that stay cooler under load tend to age better
- Repairability and replacement cost, since a cheap battery replacement extends the life of the phone
Battery health is shaped by design choices as much as daily habits. If you are weighing up different models, it can help to browse mobile phones and compare how manufacturers approach battery size, charging, and long-term support. Software support length matters here too, since there is little value in a healthy battery on a handset that has stopped receiving security updates.
Frequently asked questions
Does fast charging damage your battery?
Not immediately, but fast charging can increase battery wear over time because it generates more heat. Modern phones manage this with charging curves and temperature monitoring, but heat remains the main factor in long-term degradation.
Should you let your phone battery drain completely?
No. Regularly draining lithium batteries to zero can increase wear. Smaller, more frequent top-ups are generally better for long-term battery health than full discharge and charge cycles.
How long do phone batteries last?
Most phone batteries show noticeable capacity decline after 18 to 24 months of regular use. Heavy use, heat, and frequent fast charging can shorten this. Lighter use and cooler conditions can extend it.
How many charge cycles should a phone battery last?
Apple states that iPhone 15 and later are designed to retain 80 per cent of original capacity at 1,000 complete charge cycles under ideal conditions, where earlier models were rated to 500 cycles. Recent Pixel and Samsung flagships are rated to a similar standard. Budget handsets are frequently rated lower, sometimes between 500 and 800 cycles.
How do I check battery health on my phone?
On iPhone, go to Settings, then Battery, then Battery Health and Charging. On Samsung, go to Settings, then Battery, then Battery information. On Google Pixel, cycle count is in Settings, then About phone, then Battery information. On other Android devices, visibility varies by manufacturer.
Will phone batteries be user replaceable from 2027?
Some will. EU Regulation 2023/1542 requires user replaceable batteries on portable devices placed on the EU market from 18 February 2027, but exempts devices whose batteries retain 83 per cent capacity after 500 cycles and 80 per cent after 1,000 cycles and which carry an IP67 rating or higher. Most flagships are expected to qualify for that exemption, so the change is likely to affect cheaper handsets more than premium ones.
What battery health should a refurbished phone have?
There is no single standard, and practice varies between sellers. Ask what battery health percentage the device is supplied at, whether the battery was replaced during refurbishment, and whether the warranty covers the battery. A refurbished handset partway through its battery life is not a problem, but the price should reflect it.
Summary
Battery health describes how much capacity a battery retains compared to when new. All lithium batteries degrade over time. Heat and long periods at very high charge are common drivers of faster wear. Cycle ratings are the most useful figure for comparing how two phones will age, and current flagships are typically rated to retain 80 per cent capacity after 1,000 cycles. Fast charging is convenient, but managing heat and enabling battery protection features can help extend usable lifespan.
How we put this guide together
Manufacturer cycle ratings and battery health instructions are taken from manufacturer support documentation rather than from retailer listings or third party summaries, because the stated test conditions differ between manufacturers and matter to what the figures mean.
The regulatory information is taken from the EU battery regulation and published analysis of it rather than from manufacturer commentary. We do not carry out our own battery testing, and the degradation timescales given here are general expectations rather than measurements we have taken.
Sources and methodology
- Apple published battery information and support documentation, for the 80 per cent capacity guidance, the cycle ratings on iPhone 15 and later, and where battery health is displayed
- Samsung and Google published support documentation, for where battery information and cycle count appear on each platform
- EU Regulation 2023/1542 on batteries and waste batteries, for the 18 February 2027 date, the user replaceability requirement, the cycle and IP rating exemption criteria, and the digital battery passport
- Published technical analysis of the EU battery regulation, for how the exemption is expected to apply across premium and budget handsets
Manufacturer specifications and regulatory timelines change. Confirm the position for a specific handset with the manufacturer before relying on it.
