Low on battery? Here we review the best iPhone 6s battery cases and iPhone 6s Plus battery cases, which also work with the older iPhone 6 and iPhone 6 Plus.

The Apple iPhone 6s has a battery life shorter than most owners would like it. Who hasn’t cursed as the “Low Battery” warning pops up? For all its fancy apps and super camera the more important feature of any smartphone is its battery, for when this expires so does everything else.

Apple went for super-thinness rather than significantly better battery life when it designed the iPhone 6 and 6s. So those of us who want our phone to last all day, and then some, have to lug round a battery power bank or forgo Apple’s slimness for a bulkier battery case that will recharge a fading iPhone battery back to full life without having to stop to find a power socket.

The iPhone 6 and 6s battery cases aren't fully compatible with cases for the iPhone 7, iPhone 7 Plus, iPhone 8 and 8 Plus. Instead you can find out round-ups for those battery cases here: iPhone 7 battery cases, iPhone 8 battery cases.

If you fancy carrying a portable power pack (rather than a protective case) around with you, read our round up of the Best Portable Battery Power Banks. We've also rounded up the best iPhone 6 Plus and 6S Plus cases if you're after general protection for your device.

Many of the iPhone 6 and 6s battery cases reviewed here are very similar me-too products, but each has its own pros and cons. What has excited us are the cases tested here that show some real innovation – such as the Tylt Energi Sliding Case and Esorun iStand, that offer something more. There are also cases reviewed here that are slimmer than most, or offer massive battery capacities. And sun hats off to Mophie for offering a battery case that's also waterproof, the H2PRO.

Battery capacity can be measured in Milliamp Hours (mAh) and Watt Hours (Wh). The higher, the more charge you should get from the extra battery enclosed within the case.

ChargeTech ThinCharge

ChargeTech ThinCharge

Capacity: 2,600mAh; 9.88Wh
Weight: 70g

While supremely useful at keeping your phone working when it inevitably runs out of juice during the day or at best as the evening begins the life-saving battery case adds bulk and weight to something Apple's design team has spent years making slimmer and lighter.

So the ThinCharge is something to really celebrate. Manufacturer ChargeTech claims that the ThinCharge is the world's slimmest battery case for the iPhone 6 and 6s. We've tested a lot (!) of battery cases for the iPhone 6 and we think that this claim might just be the truth.

The ThinCharge measures a mere 11mm deep. Compare that with Mophie's most compact case, which measures nearly 15mm. Our previous slimmest battery case was the iWalk Chameleon at 12.9mm. Indeed ThinCharge adds a mere 0.69mm to the iPhone 6's depth.

It's also the lightest we've tested. At 70g it's 12g lighter than the iWalk, and 5g less weighty than the most compact Mophie case (if you think you'll notice the 5g difference).

The 2,600mAh battery should offer well over a full charge but in our tests it didn't make it much past that filling up point – to be fair this is all one really needs a battery case to do. We did find charging the case took longer than others, and the LED light charge indicator uses a system of flashes to show available charge that is not as obvious as other cases' large LED arrays.

The ThinCharge has a slight yet robust protective frame (we dropped it once and the top section came away, but snapped back on easily enough). It's a two-part case so this is quite a natural reaction to being dropped and nothing (including the iPhone) was damaged.

Not only is the ThinCharge super slim but it uses Apple's own Lightning connector to charge, which is great news as it means you don't have to muck around with fiddly micro USB cables. It won't sync via that Lightning slot, just charge the battery – to sync via cable you need to slide the phone out of the case.

While it ships in an Apple-like minimalist box it doesn't include an extra Lightning cable, but you can just use the iPhone's own, so this is no real disadvantage.

Tylt Energi Power Case for iPhone 6 and 6s

Tylt Energi Power Case for iPhone 6 and 6s

Capacity: 3,200mAh; 12.16Wh
Weight: 127g (inner layer on its own: 28g)

Pros: Clever dual-layer case so no battery bulk until you need it – but protection all the time.

Cons: Bulkier than most when both parts of case linked, but use wisely and this shouldn't matter too much.

Most battery cases are very similar with a slightly bulky back case carrying a battery of varying size, and some sort of LED lights showing you how much juice is left. The Tylt Energi Sliding Power Case is cleverer than that. It’s actually two cases: one to protect your phone when you don’t need to carry the extra battery; and the other being a more standard battery back case, here called the Power Sleeve.

The Tylt Slider – let’s call it that because it’s a better name than the one it actually has – is perfect for people who occasionally need that extra battery power to be on hand, but mostly just want a non-bulky case for phone protection.

That first, inner case is easy to fit and rather stylish, and appears robust, protecting from knocks, bumps and screen cracks. When you need the back-up battery you simply slide the first case into the second Power Sleeve.

The two cases together are bulkier than most of the others here, but that’s not the point as you only need both when heading out on a long day away from power – or when the actual recharging is taking place. Indeed you could leave the charged battery part in your bag until you need it, and then slide the two together at that moment just before your iPhone battery is due to expire.

Its 3,200mAH battery is a decent dose of juice that yields a little over one full recharge, which will be plenty for most people.

We salute the dual-layer Tylt Energi Sliding Power Case for its ingenious solution to the don’t-want-to-bulk-up-my-iPhone-but-need-more-battery-life dilemma. Battery backup without the bulk, the Tylt Slider appears to offer the best of both worlds.

iPhone 6 Plus owners can also find a version on Amazon for £48 (UK only).

Mophie Juice Pack Reserve for iPhone 6/6S

Mophie Juice Pack Reserve for iPhone 6/6S

Capacity: Up to 3,950mAh
Weight: From 75.1g

Pros: Market-leading battery case brand, quality construction made in same factories that Apple uses.

Cons: Bulkier than most and certainly not the cheapest; lacks some of the innovative features of others.

Mophie is the market leader for iPhone battery cases. What you get with Mophie is a long pedigree of quality, award-winning battery cases. From a protection point of view you can’t fault Mophie cases, which feature rubberised support pads to guard against drops and hard falls.

Mophie offers a range of battery capacities, and you can trust Mophie's claims more than the cheaper cases available online. Unlike most of the cases here the Mophie cases will sync and charge while connected to a computer. Each case comes with a Micro USB cable for charging and a headphone extension lead for those who use headphones with an angled or short jack.

The Juice Pack range has several models.

The Juice Pack Reserve is the most compact and affordable and will give your iPhone around a 60% boost, the Air should power a near-dead iPhone back to full charge, while the Plus and the Ultra will give you capacity to charge your iPhone more than once.

While the Mophies lack the innovative features seen on the Tylt Energi and slimmness of the iWalk, Mophie is a dependable brand for quality of build and effective battery life.

The 1,840mAh Juice Pack Reserve measures 7.01cm x 15cm x 1.47cm (2.76in x 5.9in x 0.58in), and weighs 75.1g (2.65oz). It's available on Amazon for £33.95/ US$37.23.

The higher-capacity and more robust 3,300mAh Juice Pack Plus measures a slightly larger 7.44cm x 15.57cm x 1.68cm (2.93in x 6.13in x 0.66in), and weighs 110g (3.9oz). The Mophie Juice Pack Plus is available on Amazon for £59.99/ $53.95.

Mophie Juice Pack H2PRO

Mophie Juice Pack H2PRO

Capacity: 2,750mAh; 10.45Wh
Weight: 114g

Pros: Waterproof; market-leading battery case brand; quality construction made in same factories that Apple uses; decent battery capacity.

Cons: Bulkier than most and certainly not the cheapest.

Another case of a battery case that goes the extra mile in terms of features or clever design is Mophie's Juice Pack H2PRO, which offers healthy extra battery life at 2,750mAh capacity plus waterproof protection. Like the Juice Pack Air it should give you a full extra charge of a fading iPhone 6/6s battery.

Water is one of the iPhone's weak spots, and a drenched iPhone is mostly declared dead, although there are ways to save a wet iPhone. So protecting your valuable device from a watery death is highly advisable. It also feels like one of the more robust designs for drops and knocks.

It's easy to put together, and also to take apart – handy as this is a case you might save just for watery environments, and use another case for everyday dry use.

The Mophie H2PRO will especially appeal to underwater photographers, divers and general beach bums or swimming pool enthusiasts. Take your phone to the beach all day and you'll likely need a battery top up, so why not invest in a waterproof battery case at the same time. You'll thank yourself for it if it gets dropped in the pool or left in a bag with a wet towel.

Emtec U500 Power Pouch

Emtec U500 Power Pouch

Capacity: 6,000mAh
Weight: 240g

Pros: Not really a case so doesn't bulk up iPhone when not being charged; interesting case alternative; large battery capacity; can charge other devices too.

Cons: Doesn't offer protection when not being charged; heavier than a normal case.

So many iPhone battery cases are similar that we rejoice when we get to test something a little different, such as the Tylt Energi Sliding Power Case, and iWalk cases.

The Emtec Power Pouch is more of a purse, in that you can slip your iPhone (there is also an Android/Windows Phone model) into a pocket and connect with the included Lighning connector only when you need to charge. For the rest of the time you can leave your iPhone naked or in a more subtle, slimline case than most of the battery cases reviewed here.

You can just leave the Power Pouch in your bag, rucksack or handbag for when you need the reserve power bank. And the 6,000mAh battery capacity is pretty huge, which could charge a fading iPhone over two times over.

There's also a standard USB port so (with the right cable) you can charge other devices from the Power Pouch, too.

Certified by Apple, the Emtec Power Pouch is well made. It doesn't really offere extra protection as it's not a case as such – although in a handbag it could protect from everyday scratches. At 240g it is a lot heavier than most battery cases, but as the iPhone doesn't need to be encased all the time it doesn't add any bulk to the phone when not in use – unlike most iPhone battery cases.

Compatible with iPhone 6s, iPhone 6, iPhone 5, iPhone 5s, iPhone 5c.

Savfy iPhone Battery Case

Savfy iPhone Battery Case

Capacity: 3,200mAh; 11.47Wh
Weight: 102g

Pros: Slim case and reasonably lightweight; high capacity battery; inexpensive

Cons: Case a little tricky to remove

The iPhone battery case market is dominated by Chinese imports, and some are better than others.

The Savfy Battery Case for iPhone 6 and iPhone 6s is one of the better battery cases available online. It’s slimmer than a Mophie but with a large battery capacity – 3,200mAh, which is just under the top Mophie’s 3,300mAh but above the less expensive Mophie battery cases.

That level of extra power should easily power up a faded iPhone for at least one full charge.

It’s a two-part design, with a solid-looking bumper and hard-shell backplate, which features a handy LED battery-level indicator. You fit the iPhone into the backplate, then snap the bumper over. Taking the bumper off was a bit fiddly, but you may not need to do this too often.

At 102g it’s around the same weight as the other recommended iPhone battery cases, although the Tylt Slider’s clever two-part design is still our favourite for lightweight protection and a separate battery case only when you need it.

Although supposedly Apple certified we did get an initial “This accessory is not certified and may not work reliably with this iPhone”. However, another push on the button and charging started immediately.

Apart from its lightweight and apparently robust design, plus decent battery capacity, the main appeal of the Savfy Battery Case is it’s online price of under £20 on Amazon.

It comes with a charging cable and pass-through jack so that angled headphone jacks will fit.

UNU DX-6 Battery case

UNU DX-6 Battery case

Capacity: 3,000mAh; 11.1Wh
Weight: 95g

Pros: Nicely designed case; easy to separate sections to remove iPhone.

Cons: Battery life not as high as others; LED display basic.

The UNU DX-6 has one of the smaller battery capacities (3,000mAh, though now you can find the 3,100mAh version using the uNu link provided above) but will still offer over a full charge for the fading iPhone. It still boasts more charge than most iPhone 5 battery cases, mind, as well as the entry-level Mophie Juice Pack Air.

When charging the case and the iPhone simultaneously from 0%, the battery case will charge for a minute or two then the phone will begin to charge. This is to protect the internal battery of the DX-6, and, UNU claims, will “dramatically increase” the total amount of charging life-cycles of the battery case.

To prevent turning the case on or off while the battery case is in a pocket or purse, the power button must be held for two seconds and then released. This avoids accidental switching on the battery, which can occur with some of the other  cases.

The case is well designed, with rubbery tough plastic for solid protection.

The usual cut-outs are included, plus you get a headphone extension cable in case you use headphones with a short or angled jack.

Lenmar Maven Battery Case

Lenmar Maven Battery Case

Capacity: 3,000mAh
Weight: 96g

Pros: Decent battery life and protection; easy to dissasemble; cool LED charge indicator; amplified sound.

Cons: Standard design; more expensive than some other Apple-acredited cases reviewed here.

The Lenmar Maven – also known as Undead Power – iPhone 6 Power Case relies on its cool, X-Men-like energy button to make it stand out from the crowd. Rather than a series of three or four LEDs the Maven's LED indicator shows charging status via flashing or solid sections of the X logo lighting up.

It's certified by Apple, and allows syncing without you having to remove your iPhone from the case.

Lenmar claims that the Maven's optimised speaker channels actually amplifues the sound from your iPhone, and the audio quality from this case did sound better than in most. It also comes with a headphone extender if you prefer to keep your music to yourself.

Other than that it's fairly standard in design, although credit must go for the ease with which the top section of the case is removed when you want to take your iPhone out. Many of the cases reviewed here require some strength and bravery in pulling the two sections apart, but the Maven's top section pulls off quite easily.

The battery is classed at 3,000mAh, which is a little higher than most, and should get you over a full charge from a dead iPhone battery.