While Apple improved the iPhone 7's battery life, you can expect it to fade quickly through the day if you're anything like the average iPhone power user. You need to boost that battery at least once during the day, and you're likely not to be close to a power outlet when you need to recharge.

There are plenty of portable power banks available – see our round up of the best power banks – but with most of these you need to lug around not just the extra battery but a Lightning or (worse) MicroUSB cable too.

The best solution is a case that includes a built-in battery. Battery cases have a dual purpose: recharge a fading phone battery when you need it most; and protect your fragile smartphone from everyday knock, drops and scratches – and sometimes worse.

The iPhone 6 had a battery capacity of 1,810mAh, compared to the iPhone 7's 1,960mAh. That's a little better but not a lot. Crucially, it's not enough for most users. Apple claims that the iPhone 7's battery will give you a couple of extra hours battery life over the day. Read our iPhone 7 review.

The iPhone 7 Plus has a 2,900mAh battery capacity, up from 2,750mAh in the iPhone 6s Plus.

The best battery cases for the iPhone 7 and 7 Plus are from Apple and Mophie, with some much-cheaper models also available from online retailers.  

(Apple hasn't yet released a battery case specifically for the newer iPhone 8 but we've rounded up the best battery cases for iPhone 8 in a separate test feature.)

The best iPhone 6/6s battery cases included the Apple Smart Case, ThinCharge, Tylt Slider, iWalk Chameleon, plus the Juice Pack range from battery-case champs Mophie. Only the Apple and Mophie versions are currently available for the iPhone 7.

It is possible to fit the iPhone 7 into an older iPhone 6 battery case, but the likelihood is that the camera cutout won't fit the iPhone 7's new camera bump properly, leading to poor photos or no photos at all.

One of the iPhone 7 battery cases reviewed here claims to be compatible with the iPhones 6, 6s and 7, due to its larger rear camera cutout, but most 6/6s cases fail the camera cutout test.

Most are, however, compatible with the later iPhone 8 - see Best battery case for iPhone 8 and iPhone 8 Plus. There aren't many yet, but we've also rounded up the best iPhone X battery cases.

Here's what to look for when choosing a battery case for your iPhone 7 or 7 Plus.

Best iPhone 7 battery cases: Power

It's not quite as simple as it sounds but look for a large battery capacity in the case. It needs to be at least 2,000mAh (milliamp hours), but that would just scrape a full recharge, and more likely give you just 80 percent more juice – enough but there's better out there. See dedicated articles on phone battery charging tips and tips to boost iPhone battery life.

Best iPhone 7 battery cases: Protection

An equally important role of the battery case is to protect your phone from bangs, crashes, drops and bumps. We look at case robustness in all our tests. Also note that while the iPhone 7 is waterproof, most cases are not.

(Also see our round up of the best iPhone 7 and 7 Plus cases).

Best iPhone 7 cases: Design

Look for lightweight and slim battery cases if you value the iPhone's naked statistics. You usually sacrifice some slimness for extra battery capacity.

Best iPhone 7 cases: Charging cable

Try to choose a battery case that uses Apple's Lightning charge and sync cable rather than MicroUSB as that avoids having to keep two different types of cable – one of which (MicroUSB) is fiddly. We also have a round up of the best charging cables if you need a few suggestions.

Apple iPhone 7 Smart Battery Case

Apple iPhone 7 Smart Battery Case
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Out the same day as the iPhone 7 – well, Apple did have an obvious advantage in getting iPhone 7 accessories out – the Apple iPhone 7 Smart Battery Case is an update on its similar product for the iPhone 6 and 6s.

It features the same odd hump on its back, which hosts the extra battery. Many people were horrified and repulsed by the somewhat clunky design – especially as everything else Apple designs wins awards for subtlety. The Smart Battery Case will not. That said, the bump on the case's back didn't bother me at all.

It is, however, a practical design, and the case feels both nice to hold and feels robust in its protective role. It has a soft-touch rubbery silicone exterior, and a soft microfiber lining that's gentle to your scratch-prone iPhone (especially the Jet Black model). At 101g it does add some weight to the phone (itself 138g), of course.

The case has a soft elastomer hinge that makes it super easy to slip the iPhone in and out of the convenient one-piece design. Many battery cases come in two parts, which can sometimes detach and get lost or snap.

You can sync and charge the iPhone 7 and Battery Case at the same time when the phone's in the case. This uses the same Lightning cable you get with the iPhone.

Unusually, the iPhone 7 draws power first from this case, before using its own internal power. Most other battery cases let the phone drain its own battery first, and then use the extra case battery. The case ensures that the iPhone will have 100 percent charge, as long as it can.

There’s no LED battery life indicator on the exterior of the case, although curiously there is one on the interior. Instead battery status is displayed on the iPhone Lock screen and in the Notification Centre. At first this seemed odd, but you get used to it quickly, and is actually a neat idea.

The iPhone 7 Smart Battery Case has a 2,365mAh charge capacity, which is lower than most battery cases but enough for one full recharge, but no more until it gets charged again itself.

At £99/US$99/€119 the Apple iPhone 7 Smart Battery Case is not cheap, but if it both protects your precious phone and gives you enough power for the day then it represents good value, and as it's made by Apple you can be sure of its build quality and safety.

Read our full Apple iPhone 7 Smart Battery Case review.

Best iPhone 7 battery cases: Mophie Juice Pack Air for iPhone 7 review

Mophie Juice Pack Air
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Mophie is the market leader in smartphone battery cases, and it's great that it now has a dedicated case for the Apple iPhone 7 and iPhone 7 Plus – as well as it's Hold Force magnetic solution (see further down this feature).

The Mophie Juice Pack Air for iPhone 7 is compatible with Qi and other popular wireless charging systems, which sets it apart from other battery cases reviewed here. Charge Force technology aligns magnetically with all Mophie Charge Force wireless power accessories (such as the Charging Base £39.95/$39.95). Simply place your Mophie case on any wireless charging base and power is sent to your device directly on contact. 

The wireless charging option is great if you buy one of the optional Mophie charging bases. It adds a level of simplicity to your day by saving you searching for the right cable and getting it into the plug the right way round.

Either wirelessly or wired the phone charges first, followed by the Juice Pack battery. The iPhone 7 model has a battery capacity of 2,525mAh, and the iPhone 7 Plus version 2,420mAh – both enough for a full recharge from a fading battery.

A battery case isn’t just there for charging purposes. It’s just as important that it protects your phone – after all, a fully charged but smashed or damaged phone is about as much use as a dead one. The iPhone 7 Mophie Juice Pack Air features rubberized support pads and raised corners to safeguard the screen from drops and scratches.

The Mophie Juice Pack Air for iPhone 7 looks and feels great. The buttons are nice and responsive.

It does add more bulk to the iPhone than some of the slimmer cases reviewed here. One disappointment is that this case charges via a Micro USB port, and not Apple's Lightning connector – meaning you have to suffer the usual non-reversible Micro USB fumbling, and need an extra cable lying around when you need it (unless you go for the wireless-charging option). It's also a two-part case design, which is not a great hardship but one-piece designs do seem more popular these days. 

Each is available in Black, Gold, Rose Gold, Navy and Red, and costs £99.95/US$99.95/€99.95 direct from Mophie, where you can also find the 7 Plus versions.

Best iPhone 7 battery cases: PEMOTech Battery Case

PEMOTech Power Bank Battery Charger Case for iPhone 6/6s/7
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The PEMOTech Battery Case claims to be compatible with not just the iPhone 7 but the 6 and 6s as well. It can do so because the rear camera cutout is large enough for the cameras on each model. (This case is not available in the US, however)

This also means you get a headphone jack port, which of course is useless on an iPhone 7, which has no such port itself. Apart from aesthetically, this doesn't matter at all.

Hooray! It uses Apple's Lightning cable to charge and sync, but the port on the case is to the right side (because of the redundant headphone port), and so you can't use wired headphones while the iPhone is in the case – even with the Lightning adapter. If you want to use headphones while using the case they will need to be wireless. See our best Bluetooth headphones reviews.

With a large 3,200mAh battery capacity this case packs a decent power punch, more than the Apple iPhone 7 Smart Battery case. However, in testing we didn't see a much greater boost than with the lower-capacity Apple case – sometimes only 90% of a full recharge.

The design is a two part construction, which you should be careful not to lose or break the upper part, although you shouldn't need to take it apart very often as you can both charge and sync the phone in the case.

Unlike the Apple Smart Battery Case it does feature an on/off button and four LED lights to indicate remaining case power. The case is backup power, as the iPhone uses its own battery first, and then relies on the case for a recharge. In some ways we prefer this method as it's nice to know you have a full backup in the case while the phone runs down.

That said, we do prefer it when charging both case and phone at the same time for the phone to be charged first and battery case second. The PEMOTech iPhone 7 battery case is supposed to charge itself first, then the phone. In practice we found that it often charged itself, but then forgot to charge the phone afterwards. That means you either have to immediately use the case to charge the phone, or charge the phone separately when near a power source. It's a pain but it works.

The case feels robust enough, despite the two-part design, and even features a little kickstand so you can prop the phone up on a flat surface when watching videos.

Our major concern is that the case is not certified by Apple, and the super-cheap price tag (we've seen it for under £15 online) does make us wonder if it's really too good to be true! It probably is because we got less than a 100% charge out of what is meant to be a 3,200mAh battery, and it charges the case and not the phone when plugged in.

That said, this case is so cheap it can shrug off these weaknesses.

Read our full PEMOTech iPhone 7 Battery Case review.

Best iPhone 7 battery cases: Mophie Charge Force

Mophie Charge Force Case for iPhone 7 and 7 Plus
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The Mophie Charge Force Case isn't a battery case in itself, but it does allow wireless charging via Qi and virtually any wireless charging technology. It's an interesting alternative to always carrying a heavier battery case with you at all times.

From a power point of view you can attach a Charge Force Powerstation Mini battery pack magnetically to the case. This means you can use the lightweight case (48g)(£59.95/US$59.95) for everyday protection and wireless charging when you need it. When you need more power on the go, you can attach the weightier (90g) 3,000mAh Charge Force Powerstation battery pack (£39.95/US$49.95).

You can find the 7 Plus version for £59.99 in the UK.

Best iPhone 7 battery cases: Mophie Hold Force

Mophie Hold Force Powerstation Plus Mini
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The Mophie Hold Force series is another Mophie family of attachments that cling magnetically to the Hold Force Base Case (£39.95/US$15.95), which is compatible with both iPhone 7 and iPhone 7 Plus. If you prefer a proper Mophie case then see the Juice Pack Air, reviewed above – or the midway Charge Force Case and battery accessory.

There's a Wallet and wraparound Folio to holds cards and cash, but what interests us here is the (take a deep breath) Mophie Hold Force Powerstation Plus Mini – a power pack that magnetically attaches to the Hold Force base Case. You can see Mophie's base case options here.

Its 4,000mAh capacity beats the other iPhone 7 battery cases, and promises 12 extra hours of iPhone use.

It features built-in Lightning and Micro USB connectors, so you don't need to carry a spare Lightning cable with you.

But this is not a proper battery case. The magnetic connection isn't strong enough to stay on while the phone is in use, and the battery pack covers up the rear camera when attached.

This is a useful product to charge up a fading iPhone but it's not as handy as a proper case, or indeed as useful for wireless charging. You also need the Base Case on your phone at all times.

The price starts to mount up when you add the Base Case (£19.95/US7.95/€19.95) and the Powerstation Plus Mini (£59.95/US$59.95/€59.95). For that price you're close to the Apple iPhone 7 Smart Battery Case, which has less juice but is much easier to use.

Rather than the Hold Force solution we suggest just buying one of Mophie's universal Powerstation power packs with integrated cable. You can browse options here (US readers can go here).