How to know when it's time to replace the battery on your phone

Which? research has revealed that deteriorating batteries are often the most common fault affecting smartphones. But batteries are usually the cheapest part of a phone to replace and can be the easiest way to delay your next pricey upgrade.

Read on to find out if a new battery can breath new life into your phone, and discover some tricks to lengthening its life.

Our guide to the best smartphones to buy in 2026 reveals the models that aced our lab tests. 

First, check your phone's battery integrity

Battery capacities naturally deteriorate over time and checking your phone's battery integrity percentage will tell you if replacing it might improve battery life. The lower the percentage, the lower the battery's capacity. 

It only takes a couple of seconds to see if your phone's battery is struggling to keep up like it used to. It's generally recommended that a battery capacity of 80% or more is healthy.

How to check your battery health on iPhones

Go to Settings > Battery > Battery Health and Charging. Here you can see the current maximum capacity of your battery and a few more useful settings worth looking at.

How to check your battery health on Android phones

It's not as straightforward with Android phones, since different manufacturers have a slightly different setup, but it has gotten easier than it used to be. With Android 16, most Android phones let you monitor battery health by going to Settings, Battery, then Battery Health – pretty simple. Samsung users can check battery health through the phone diagnostics on the Samsung Members app. Free third-party apps like Accubattery, downloadable from the Google Play store, can also be a quick and easy way to check battery health.

Is replacing the battery your best option?

Most manufacturers say that a phone battery is worth replacing when its integrity drops below 80%. Some (such as Apple) will replace it for free under their warranties if it drops this low before it's a year old. But most batteries don't worsen drastically until they are much older, and they are usually inexpensive to replace. This delays the need to buy a new phone and is a more environmentally-friendly choice.

However, before buying a replacement battery, weigh up how old your phone is and when software support will end. We don't recommend you continue to use a device for long without the security updates that keep your data safe – our phone support calculator effectively gives you a 'best before' date for your device. If this date is coming up in the next year, we'd generally recommend you consider upgrading instead of replacing your current phone's battery.

It's also worth bearing in mind that other factors can shorten your phone's battery life beyond your control. Software updates sometimes deliver new features that require more power to work efficiently.

You don't have to buy a flagship phone for £700 or more to get a real performer – our mobile phone reviews reveal Best Buys from just £340, and Great Value phones for as little as £130. You can also check our guides to the best iPhone deals and best Android phone deals for a bargain on a new handset.

How long should a new smartphone battery last?

Manufacturers generally say that a battery should not drop below 80% health until you've hit at least 800 full charges (i.e. from 0% to 100%), and many do better for longer. For most people, this would equate to at least a couple of years, so if you plan to keep the phone for this amount of time, replacing the battery can put it back in tip-top shape for the duration.

How much do mobile phone battery replacements cost?

This can vary depending on two factors: who you buy the new battery from and which model of phone you have. You can get the battery replaced directly from your phone's manufacturer, or through a reputable third-party retailer (such as Fixfactor, iSmash, Square Repair or Timpson).

For example, an official Apple battery replacement for an iPhone 16 will cost an estimated £95, and an iPhone 15 is also £95. But third-party retailer iSmash will charge just £49 for these. However, the parts used mean you will lose access to battery health tracking features. It will cost you more (£149) to have iSmash repair one of these iPhones for you and maintain the tracking.

There's further evidence that buying the manufacturer's direct repair isn't always more expensive. Samsung Repair charges £59 for a new Samsung Galaxy S25 battery, and iExpertRepairs also charges £65. 

For maximum savings, the Fairphone 6 is the benchmark for repairability, with a new genuine battery available for just £35, and it's possible to replace it yourself with just a single screwdriver.

Before buying, double-check that the cost of the battery includes a professional installation. We explain more in our guide to Mobile phone repair: how to fix your smartphone

Prices correct in February 2026.

Five quick tips to boost battery life on a mobile phone

There are ways to boost battery life without shelling out for a new phone or a new battery. Try these first to see if it helps. You can find more tricks in our guide on 9 easy ways to improve battery life on iPhone and Android

1. Enable battery saving mode

You've likely seen a request pop up on your phone to enable battery saving (or low power) mode once it's only got 20% of battery left. This mode limits certain background features that can drain your battery. 

In 2026, software has become even smarter; iOS 26 now includes Adaptive Power, which intelligently trims performance throughout the day based on your habits, rather than the hammer of standard Low Power Mode. Android 16 users can also benefit from Battery Health Assistance, which automatically adjusts charging voltage to stabilise the battery's ageing process after its first 200 charging cycles.

2. Change your screen settings

Some of the latest premium smartphones have screens that can get incredibly bright, which can have a big impact on the battery life. Decrease it when you can or use auto-brightness. 

Since many 2026 phones use OLED screens, enabling Dark Mode is a powerful trick — it physically turns off black pixels to save energy. It's also worth checking your connectivity; enabling 5G Auto or Smart Data mode allows your phone to switch to LTE when high speeds aren't needed, saving significant power in areas with a weak 5G signal

3. Invest in a power bank

A power bank is a handy portable charger that can keep your phone's battery full of juice when you're on the go. See which models impressed in our tests of the best power banks and portable chargers. 

Look for Qi2-certified power banks; these snap magnetically to your phone to ensure perfect alignment, which prevents energy from being wasted as heat during the charge.

4. Invest in a fast charger

Every phone has a different wattage limit when it comes to charging, and the higher the wattage, the quicker it charges. The biggest shift in 2026 is Qi2 wireless charging, which now hits 25W speeds – fast enough to rival a wired plug while keeping the battery cooler than older wireless pads. 

To keep things efficient, invest in a GaN (Gallium Nitride) adapter; these are smaller and generate much less heat than older silicon bricks, which helps protect your battery's internal chemistry in the long run – see our guide to fast chargers for more.