It may have been well over three years since the iPhone 8 and 8 Plus were released, but they remain very capable and popular phones. 

They were the last smartphones to come with Touch ID, with the iPhone X launched alongside it ditching the fingerprint scanner altogether. 

The iPhone 8 has just a 1821mAh battery, while the 8 Plus comes with 2691mAh. While its true that Apple's synergy between hardware and software means it's not as reliant as Android on battery capacity, it's hard to believe that will be enough for most people. 

Apple claims its software optimisations will get you 12 and 13 hours of battery life respectively, but that number will vary hugely depending on the apps and features you use, and may decline soon after purchasing your new phone. 

As a result, 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 portable power bank, but usually that means carrying around an extra cable, too – and taking up valuable bag or pocket space.

In that case (no pun intended), your best option is a battery case. That way, you can charge your phone while continuing to use it like normal.

Many options will still allow you to continue using wireless charging, a feature Apple introduced on the iPhone 8 and 8 Plus. Here's our round-up of the best battery cases for the iPhone 8, 8 Plus or both.

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 £79.20 (approx US$102.21).

Kilponen 8500mAh Battery Case for iPhone 6 Plus/6s Plus/7 Plus/8 Plus

Kilponen 8500mAh Battery Case for iPhone 6 Plus/6s Plus/7 Plus/8 Plus

Kilponen's battery case provides a significant battery boost in the thinnest possible package. It does a good job, too, with the 8500mAh able to fully charge your iPhone 8 Plus more than four times. 

It adds just 2.6cm of bulk to your device, meaning you won't notice it in the same way you do with some high-capacity battery chargers.

You can easily keep the case on all day, turning it on when you need it, but at 200g it won't weigh you down if you need to throw it in a bag. 

In terms of protection, the case provides 360° support thanks to a specially designed frame and smooth hardened plastic design. 

It uses the standard four lights on the back of the case to indicate how much charge is left, each light equalling 25% battery. 

Apple's stubborn design choices between 2014 and 2016 also means this case will work with the 6 Plus, 6s Plus and 7 Plus. 

You can buy it now for £25.95.

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 and 2,525mAh for the iPhone 8. This lower capacity case should provide up to another 60% battery life, while the larger capacity battery should recharge your iPhone 8 Plus completely.

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.

Tryswyop 6000mAh Battery Case for iPhone 6/6S/7/8

Tryswyop 6000mAh Battery Case for iPhone 6/6S/7/8

Upon first impressions, it's hard to imagine that there's a battery built-in the the Tryswop case. At just 18.5mm thick, it's among the thinnest battery cases you can find. 

The 6000mAh capacity means you can easily get three full charges from this case, while the LED lights on the outside mean you can see how much is left at a glance. Next to it is a simple on/off switch, putting you in control over whether you need a battery boost. 

This case is equally adept at protecting your phone, with raised edges and a hard-shell design ensuring it survives any drops or scrapes too. What's more, if you'd ever like to swap this out for a different case, installation is as simple as sliding your phone in and plugging it into the lightning cable. 

AOPAWA Battery Case for iPhone 6 Plus/6s Plus/7 Plus/8 Plus

AOPAWA Battery Case for iPhone 6 Plus/6s Plus/7 Plus/8 Plus

Like many entries in this round-up, AOPAWA's battery case is compatible with iPhone 6 Plus, 6s Plus, 7 Plus and 8 Plus. 

At 8500mAh, it can easily provide your phone with at least three full charges. It also comes with sync-through technology, meaning both your phone and the case can be charged at the same time. 

It case fulfils its purpose as a method of protection, with tough build materials and a 360 degree scratch guard. 

What's more, despite packing a huge battery, this case will still add relatively little bulk to your device.

While we can easily recommend it, there's the added peace of mind that the case comes with a 24-month warranty.