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

As many modern smartphones boast huge batteries, the 1715mAh cell on 2015's 6s won't last as long as many owners would like it to. 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 (see the Apple Smart Battery Case for iPhone 6s, £95.41, UK only)

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. See our separate dedicated round-ups for iPhone 7 battery cases and 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.

Most phone batteries are measured in milliampere hours (mAh). The higher, the more charge you should get from the extra battery enclosed within the case.

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

The kilponen battery case provides an additional 6,000mAh of juice with minimal bulk, while also protecting your phone. 

While it is heavier than the phone itself at 204g, it should be able to fully charge your phone more than three times. When plugged in, it charges both your iPhone and the battery pack at the same time, so you don't have to remove the case. It's compatible with Apple Pay, too. 

LED lights on the back also indicate how much power is left in the battery pack, and there's Apple Pay compatibility too.

.You can buy it on Amazon for £28.95, where you'll also get a 2-year warranty and the option for a full refund within 90 days of purchase. 

Mophie Juice Pack Reserve for iPhone 6/6S

Mophie Juice Pack Reserve for iPhone 6/6S

You can always rely on Mophie's for solid iPhone battery cases. From a protection point of view you can’t fault them, as they feature rubberised support pads to guard against drops and hard falls.

The Juice Pack Reserve (£43.39/US$59.95) on Amazon US) is the most compact and affordable and will give your iPhone around a 60% boost at the touch of a button.

The 1,840mAh Juice Pack Reserve weighs just 75.1g, so it won't add much bulk to your device. 

Emtec U500 Power Pouch

Emtec U500 Power Pouch

The Emtec Power Pouch is more of a purse, in that you can slip your phone into a pocket, 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 offer 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 it can easily be detached when not in use. 

You can buy it now for £19.88/US$31.99.

Savfy iPhone Battery Case

Savfy iPhone Battery Case

Savfy's battery case is 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.

The 3200mAh cell means it should fully charge your device at least 1.5 times, while at 102g it's pretty typical of an iPhone battery case. 

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.

It comes with a charging cable and pass-through jack so that angled headphone jacks will fit. This case usually retails for under £20, but it's not currently available. 

UNU DX-6 Battery case

UNU DX-6 Battery case

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.   

You can buy it for £61.97/US$79.95.