Apple claims a battery life of 12 hours for its new iPhone 8 and 13 hours for the iPhone 8 Plus, but, depending on the apps and features you use, that number is going to go down faster than you expect.

Many of our phones start to fade too early in the day, and it’s rarely convenient to recharge while you’re on the move – even with the addition of wireless charging.

You can buy yourself a power bank (portable battery charger), but usually that means carrying around an extra cable, too – and taking up valuable bag or pocket space.

The answer is a battery case, and Apple’s latest iPhone 8 and iPhone 8 Plus are crying out for a protective case that also keeps the phone going when the battery inevitably starts to fade.

Both front and back of the iPhone 8 and 8Plus are now made of glass – to allow for wireless charging – which makes protection as important as battery life, which is where a battery case comes into its own.

Apple has raved about the efficiency of its new A11 Bionic chipset – saying it’s 70 percent more efficient while idle than the A10 in the iPhone 7 and 7 Plus. But even Apple’s own comparison page exposes the fact that 7 vs 8 battery life is “about the same”.

It turns out that Apple has actually reduced the size of the batteries in both the iPhone 8 and iPhone 8 Plus.

The iPhone 8 has a 1,821mAh (milliamp hours) battery, which is 7 percent smaller than the iPhone 7’s 1,960mAh battery. The iPhone 8 Plus has a 2,691mAh battery, which is the smallest capacity ever seen in the Plus range and 8 percent smaller than the battery in the 7 Plus (2,900mAh). With Apple caring little for battery life yet again, both the iPhone 8 and iPhone 8 Plus will definitely do more for you wrapped up in a battery case and having its new glass back protected.

Of course, covering the 8’s glass back could nullify the wireless-charging option, but some cases allow for this and retain the wireless functionality. See Best Wireless Chargers for iPhone.

As the iPhone 8 isn’t so different to the iPhone 7 (and the same goes for the 8 Plus and 7 Plus) it’s possible to fit the newer 8 into a case for the older 7. This is useful as currently there are few dedicated iPhone 8 battery cases.

Here’s our round up of the best battery cases that work with the iPhone 8 and iPhone 8 Plus.

Apple iPhone 7 Smart Battery Case

Apple iPhone 7 Smart Battery Case
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While Apple doesn’t sell a Smart Battery Case for either the iPhone 8 or 8 Plus, it does sell them for the iPhone 7 – but not the 7 Plus.

We slipped an iPhone 8 easily into Apple’s iPhone 7 Smart Battery Case with no problems. The camera at the back isn’t impeded, and all the buttons work just fine.

Some people hate the looks of the Smart Battery Case, with its humped back, but we love its one-piece design and the way it charges the phone all the time rather than waiting for you to switch on charging from the case. Obviously, it’s all properly certified by Apple!

At 102g it’s lightweight but will obviously add some bulk to the normally anorexic iPhone.

You can see how much charge is left in the case by swiping right on the iPhone home screen. There aren’t any lights on the case itself, although there is one inside so you know it’s charging itself when plugged in without the phone.

It charges and syncs through a Lightning slot so there’s no need to mess around with fiddly Micro USB cables.

There’s easily enough charge to get you through over a day’s heavy usage.

My own Apple Smart Battery Case (used with an iPhone 7) already has a couple of nicks in it – proving that it also does a good job of protecting the iPhone from knocks and drops.

While Apple has relisted some of its iPhone 7 cases as now iPhone 8 / 7 it hasn’t relabelled the Smart Battery Case. This maybe because it’s planning a version that retains the wireless functionality, but it’s odd that this wasn’t ready at the 8 launch date.

It’s available in Black, White and a lovely Red, and costs £99/$99/€99, direct from the Apple Store.

Mophie Juice Pack Classic

Mophie Juice Pack Classic
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Mophie is the biggest name in smartphone battery cases, and its products are top notch, although more expensive than many of the battery cases you’ll find coming out of China on Amazon.

Mophie is planning new battery cases for the 8 and 8 Plus, but doesn’t yet sell any from its website. However, it does sell one on the Apple Store – the Mophie Juice Pack Classic for iPhone 8 /7, and Juice Pack Classic for iPhone 8 Plus / 7 Plus. All are Apple certified.

In our tests the new 8 and 8 Plus will fit and work fine in the Juice Pack Air for iPhone 7 / 7 Plus cases, which are sold on the Mophie store.

Both Juice Pack Classic (£79.95/$99.95) and Juice Pack Air (£89.95/$99.95) have the same power capacities: 2,525mAh for the 7 / 8; and 2,420mAh for the 7 Plus / 8 Plus. Both should be enough for close on a full recharge of the fading iPhone battery.

For the extra £10/$xx you spend on the Air you get wireless charging through the case. With the Classic you’d have to remove the iPhone 8 from the case to charge wirelessly, and the case itself would have to be charged with the included Micro USB cable.

While the Apple Smart Battery Case fills the iPhone as its battery fades, the Juice Packs wait for you to initiate the recharge – via the button at the back of the case, which also has four LED charge indicator lights so you know how much power is left in the case.

The Mophie Juice Pack feels a little bulkier than the Apple Smart Case, but offers robust phone protection.

Unlike the Apple case you use a Micro USB cable (included) to charge up the Classic case, although the Juice Pack Air can charge wirelessly or via Micro USB.

The Classic (Black only) weighs 99.5g, while the Air (Black, Gold or Rose Gold) is slightly heavier at 103.3g.

Marsno iPhone 7 / 8 Battery Case

Marsno iPhone 7 / 8 Battery Case
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You can find much cheaper battery cases than the official Apple and Mophie cases (both Apple-certified) reviewed here.

The Marsno Battery Case can be found for £33 on Amazon UK ($30 on Amazon.com for the White version), and features a larger capacity (3,000mAh) battery too. In our tests it easily recharged an iPhone from under 10% to full.

As with the other cases tested here the buttons and camera work fine within the case, which will also work with iPhone 6, 7 and 8.

It’s a neat one-piece design, much like the Apple but with a less pronounced hump, and weighs 95g so is at the light end of the battery cases in this roundup.

Also like the Apple case this charges with a Lightning cable (not included), which we prefer to fiddly Micro USB. The actual Lightning connector, however, doesn’t look official but does work. If the Lightning was Apple certified we'd have scored this inexpensive but well-made case even higher.

Anker PowerCore Case for iPhone 7

Anker PowerCore Case for iPhone 7
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Another case that works with all (non-Plus-sized) iPhones from the 6s through to the 8 is the Anker PowerCore that features a large back camera cutout across the width of the phone.

Its battery capacity is 2,200mAh – above the iPhone 8’s own battery but a little below the Apple and Mophie cases. But it is Apple certified, unlike some of the battery cases tested here that offer larger capacities.

The one-piece PowerCore feels much like the Apple case, and is actually one of the lightest we tested, at just 84g. However, it connects to the iPhone not though a static integrated Lightning connector but via a dangly cable that you plug in when you need to recharge the phone from the case.

The Anker PowerCore is a lot cheaper than the Apple Smart Case - it’s just £29.99 on Amazon UK and $33.99 on Amazon.com.

The case itself charges via MicroUSB cable (included).

Runsy iPhone 8 /7 / 6s / 6 Battery Case

Runsy iPhone 8 /7 / 6s / 6 Battery Case
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Much heavier and a fair bit bulkier is the Runsy Battery Case, which weighs in at 139g.

This extra heft is no doubt due to the giant 5,800mAh battery capacity. We were surprised to see the manufacturer describe it as an “ultra-slim design”!

The case is a two-part design, which we found a little fiddly, but the phone should live inside the case most of the time so shouldn’t be a problem. We also weren’t rather concerned by the internal unofficial-looking Lightning connector that looked like it would impale the iPhone’s charging slot. The case did charge the phone, though.

The big case features a little stand so you can use it to prop up the phone when watching a video, and also a fully sized USB slot that can be used to attach a second phone so that you can charge two at once!

At £30 on Amazon UK and $35 on Amazon US for iPhone 8, and £35 UK and $40 in the US for 8 Plus, it’s certainly one of the cheaper battery cases that works with the iPhone 8, but it’s a big old brute of a case.

The Runsy might appeal to the long-haul traveller or very demanding users who require such a large backup battery during the day, but for casual users who want a little extra battery life plus phone protection this is probably over the top.

Nektech iPhone 7 / 8 Battery Case

Nektech iPhone 7 / 8 Battery Case
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The Nektech battery case does feature an Apple-certified Lightning connector, which is more reassuring than the other cheaper cases we tested.

Its 3,100mAh battery capacity should give you a full recharge, but is not as giant as the other cheaper cases here – but bigger than the Apple and Mophie battery cases.

It’s one-piece design is at the bulkier and heavier (111g) end of the range.

At 15.5cm it is by far the longest of the battery cases we tested, with the Apple case measuring 15cm and the Marsno just 14.3cm. if used just for travelling rather than everyday use then you shouldn’t balk at this added bulk.

There’s an LED strip at the back to let you know how much charge is left in the case. You recharge via a MicroUSB cable (included).

The Nektech Battery Case costs £26 on Amazon UK and $40 on Amazon US for iPhone 8; for the 8 Plus model its costs £30 in the UK and $50 in the US.