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.

If you've been coughed up for the iPhone X, take a look at the options for best iPhone X 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

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 iPhone 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 slim 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. Long-term testing did suggest that the case begins to tear at the edges after about a year, and we saw this degradation on a couple of Apple cases. That said, we were tempted to buy from Apple again.

While Apple has relisted some of its iPhone 7 cases as now iPhone 8 / 7 it hasn’t relabelled the Smart Battery Case.

It’s available in Black, White and a lovely Red, and costs £99/$99/€99, direct from the Apple Store or pick it up from Amazon UK for around £95//US$99.

Mophie Juice Pack Air

Mophie Juice Pack Air

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's Juice Pack Air wireless charging battery cases (hence 'Air') has a capacity of 2,525mAh for the iPhone 8 Plus (£99.95) and 2,525mAh for the iPhone 8 (£99.95/$99.95). This lower capacity case should provide up to another 60% battery life, while the larger capacity battery should recharge your iPhone 8 Plus completely.

Pick up the Juice Pack Air for iPhone 8 for £99.95 from Mophie, or from the Apple Store for £89.95/US$99.95, where you can also find the 8 Plus model. It's also on Amazon at nearly half the price at £44.95 (iPhone 8 model, $99.95 in the US). These are compatible with 7/7 Plus models too, respectively.

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.

Moment Battery Photo Case

Moment Battery Photo Case

We love a product with a difference, and the Moment battery case is just such a thing. It’s a battery case to which you can fit a variety of camera lenses, and it works very well.

First, the battery part. It’s a one-piece rubberized design, which we prefer. You slip the iPhone 7/8 or 7/8 Plus in by bending back the top part. We did find that it was a tight fit for our iPhone 8, and had to pluck at the edge to get it slipped in snuggly.

The case (black speckled) has a battery capacity of 2,500mAh for the iPhone 8 and 3,800mAh for the Plus, which should be enough to get you through a whole day by adding another 90 percent of full phone power. It powers by Lightning cable, which is more convenient and less fiddly than the Micro USB you find on many battery cases.

You can see the remaining battery charge in the Moment app, which you need to download from the App Store. The app also lets you control the shutter, though there's a physical shutter button built into the case itself.

The two-stage camera shutter button (half-press to find focus and full-press to capture) works in the Moment App or in the iPhone Camera App. In the app you can opt to shoot your photos in RAW, TIFF, or JPG formats, adjust and lock the focus on your image, and change important settings like photo temperature and exposure on the fly. 

The case feels rugged enough to protect your phone from the usual knocks and drops, so from a power and protection point of view it works very well.

The Moment Battery Photo Case, though, keeps its magic for the photographer, who can make their iPhone into a DSLR. It’s a cinch to fix the lenses to the case (just rotate and click), which is not what we’d experienced with other case lens systems.

You can buy a super fisheye lens ($99.99/£96.71, on Amazon), anamorphic lens ($149.99, on Amazon US; around £118 from Moment), wide lens ($119.99 on Amazon; around £95 from Moment), teleportrait lens ($119.99, on Amazon US; around £95 on Moment), and a macro lens ($99.99 on Amazon; around £79 from Moment). Sure, these aren’t cheap, but they are very well made, if a little heavy. They come with smart little holding cases. Quality is great, too – read the full review on our sister site Macworld US.

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

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

Much heavier and a fair bit bulkier is the Runsy Battery Case, which weighs in at 137g. This extra heft is no doubt due to the giant 5,800mAh battery capacity.

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.

In fact, you can charge a second phone while your iPhone 8 charges, using the USB cable (not included).

At £25.99 on Amazon UK for iPhone 8, it’s certainly one of the cheaper battery cases, 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.

It's currently unavailable in the US.

Nekteck iPhone 7 Plus / 8 Plus Battery Case

Nekteck iPhone 7 Plus / 8 Plus Battery Case

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

Its 4,000mAh battery capacity should give you a full recharge. It's not as giant as the Runsy cases here – but bigger than the Apple and Mophie battery cases.

It’s one-piece design is at the bulkier and heavier (227g) end of the range. 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 roughly £26 on Amazon UK and $19.99 on Amazon US for iPhone 8 Plus.