Why is it that your phone's battery seems to get worse over time? At first it might have power to spare as you snuggle into bed at the end of the day, but as time goes on you find your battery is just half-full by lunchtime.

Partly it's how you use your phone - the apps you install, the junk you collect, the customisations you make, and the more and more notifications you receive - puts more strain on the battery. (Read our tips on how to extend battery life.)

But the other thing to consider is that phone batteries, like all batteries, do degrade over time, which means they are increasingly incapable of holding the same amount of power. While they should have a lifespan of between three and five years, or between 500 and 1,000 charging cycles, a three-year-old phone battery is never going to keep going as long as a brand-new battery.

Three things wear out lithium-ion batteries: number of charging cycles, temperature, and age.

However, armed with our tips for best battery care practice, you can maintain your smartphone battery health much longer.

When should I charge my phone?

The golden rule is to keep your battery topped up somewhere between 30% and 90% most of the time. Top it up when it drops below 50%, but unplug it before it hits 100%. For this reason, you might want to reconsider leaving it plugged in overnight.

Pushing in the last charge from 80-100% causes a lithium-ion battery to age faster.

Maybe it's better to recharge in the morning instead, at the breakfast table or on your office desk. That way, it is easier to keep an eye on the battery percentage during charging.

iOS users can use the Shortcuts app to set a notification when the battery level reaches a certain percentage. This is done under the tab "Automation" and then "Battery Level".

Giving your phone a full recharge is not fatal for a phone battery, and it seems almost counter-intuitive not to do so, but giving it a full recharge every time you charge it will shorten its lifespan.

Likewise, at the other end of the scale, avoid allowing your phone battery to get below 20%.

Lithium-ion batteries don’t feel good about going too far below the 20% mark. Instead, see the extra 20% "at the bottom" as a buffer for demanding days, but on weekdays start charging when the warning for Low Battery level appears.

In short, lithium-ion batteries thrive best in the middle. Don't get a low battery percentage, but also not too high.

Should I charge my phone battery to 100%?

No, or at least not every time you charge it. Some people recommend that you do a full zero to 100% battery recharge (a "charge cycle") once a month - as this re-calibrates the battery, which is a bit like restarting your computer.

But others disregard this as a myth for current lithium-ion batteries in phones.

To keep your long-term battery life in good health, frequent, small charges are better than full recharging.

With iOS 13 and later, Optimised Battery Charging (Settings>Battery> Battery Health) is designed to reduce the wear on your battery and improve its lifespan by reducing the time your iPhone spends fully charged. When the feature is enabled, your iPhone should delay charging past 80% in certain situations, depending on Location Services that tell the phone when it is at home or work (when you are less likely to need a full charge) compared to when you are travelling.

The deeper you discharge a lithium battery, the more stress is inflicted on the battery. So, topping up frequently extends battery life.

Also see: Best power banks

Should I charge my phone overnight?

As a rule, it's best to avoid, despite the convenience of waking up with a full battery in the morning. Each full charge counts as a 'cycle', and your phone is only built to last for a set number. 

If you charge overnight, you are guaranteed to miss when the phone exceeds the magic 80% mark that is best for extended long-term life.

While most modern smartphones have built-in sensors to shut off charging when they hit 100%, if still turned on they will lose a small amount of battery while idle.

What you may get is a “trickle charge” as the charger attempts to keep the phone at 100% as your phone naturally loses on its own charge during the night. This means that your phone is constantly bouncing between a full charge and a little bit below that full charge - 99% to 100% and back again during a longer-than-required charge. It can also heat the phone up, which is also bad for the battery.

So, charging during the day is better than charging overnight.

Your best policy is to have Do Not Disturb and Airplane Mode switched on. Better still, you could completely switch off your phone, but that may not be possible if you rely on it as an alarm or wish to be ready to take calls at all hours. 

Some devices are also set to power up once the cable is connected by default. Even during waking hours, it's best to catch your phone before it hits 100%, or at least not leave the charger supplying charge to an already full battery for too long. 

If you are leaving it plugged in for a long period of time, removing the case can prevent it over-heating.

Will fast-charging damage my phone?

The majority of modern smartphones support some form of fast-charging. However, this often requires you to purchase an additional accessory. The industry standard is Qualcomm's Quick Charge, which delivers 18W of power.

However, many phone makers have their own fast charge standard, many of which can deliver even faster speeds by adjusting power management code to request a higher voltage charge is sent. Samsung is now even selling a 45W charger!

While fast-charging itself will not harm your phone's battery, which is built to support it, the heat generated will potentially affect its lifespan. So it's on you to balance the advantages of faster charging with the convenience of quickly topping up your phone before you dash out the door.

In the same way that phone batteries don't like extreme heat, they also don't like the cold. So it goes without saying that you should avoid leaving your phone in a hot car, on the beach, next to the oven, out in the snow. Typically, batteries perform at their optimum somewhere between 20 and 30°C, but short periods outside of this should be fine. 

Can I use any phone charger?

Where possible use the charger that came with your phone, as it is sure to have the correct rating. Or make sure that a third-party charger is approved by your phone's manufacturer. Cheap alternatives from Amazon or eBay may harm your phone, and there have been several reported cases of cheap chargers actually catching on fire.

That said, your phone should draw only the power that it needs from a USB charger.

Also see: Best USB Chargers for your phone and Best Wireless Chargers.

Battery memory effect: Fact or fiction?

The battery memory effect concerns batteries that are regularly charged between 20% and 80% and suggests that the phone might somehow 'forget' that extra 40% you routinely ignore.

Lithium batteries, which are in the majority of modern smartphones, do not suffer the battery memory effect, though older nickel-based (NiMH and NiCd) batteries do.

Nickel-based forget their full capacity if they aren’t discharged and charged from 0 to 100%. But, habitually cycling your lithium-ion battery from 0 to 100% will adversely affect its battery life.

Avoid Parasite Loads

If you charge your phone while using it - for example, while watching a video - you can "confuse" the battery by creating mini-cycles, during which parts of the battery continually cycle and deteriorate at a faster rate than the rest of the cell.

Ideally, you should turn your device off while charging. But, more realistically, just leave it idle while charging.

Keep the phone battery cool

As you might expect, heat is a battery's enemy. Don't let it get too hot or too cold - especially when charging. If a phone gets too hot, you will be damaging its battery, so try to keep it cool where possible.

Charging the phone from a power bank on the beach in a deckchair is a worst-case scenario for battery health. Try keeping your phone in the shade if you need to charge on a hot summer day. Charging by a window can also lead to excess heat. Read how to cool down a hot iPhone.

The cold is also not good for batteries either. If you come in from a long walk in the winter cold, let the phone reach room temperature before you plug in the cable.

Heat and batteries do not belong together. Batteries are a bit like humans, at least in the narrow sense that they thrive best around 20-25 degrees.

Storing battery tips

Don’t leave a lithium battery lying around too long at 0% - if you're not using it for a while, leave it with around 50% charge.

If you are going to put the phone away for a long time, first charge it to somewhere between 40-80% and then turn off the phone.

You'll find the battery will drain between 5% and 10% each month, and if you let it discharge completely it might become incapable of holding a charge at all. That's probably why an old phone's battery life is so much worse after a few months in a drawer, even when it hasn't been used. 

More tips for longer phone battery life

• Use the power save mode more often. It reduces power consumption and thus reduces the number of cycles.

• Try your screen's Dark Mode, as the phone turns off the pixels displaying black, This means you save battery life when the white panels go dark. Or just turn your phone's brightness down!

• Turn off background updates for apps you think don't need them - it also reduces power consumption.

• Turn off or put the phone in Airplane Mode when you don’t need it, such as overnight - preferably with a reasonable battery level left.

• Don’t force quit the apps. Your phone’s operating system is best at pausing the apps that aren’t needed - it uses lower power consumption than a "cold start" for each app again and again.

Additional reporting by Samuel Nyberg.