The PwrVault iPhone 4 Battery Case might not seem like the obvious choice to dress your trendy Apple smartphone – because as well as protecting the device, it also makes it look a bit bigger. Thankfully, that’s not the only depth it adds…

The case from iPowerUp has one very important talent that will have you snapping it on with barely a worry about any size zero issues – it works as an additional rechargeable battery that increases the life of your iPhone.

The case comes in two parts and easily slots onto the phone, connecting to a computer with a USB cable to charge up its extra battery. That same connection works double duty to sync the phone with your computer using the USB cable, so no need to remove the case to slot it into a dock.

All of the access points on the phone – on/off switch, volume, headphone jack, etc – can be reached as usual (this is the same with the iPhone 4S, which Apple fact fans will know has a very slight difference when it comes to the placement of the ringer and volume buttons). Only the docking port remains out of bounds because that’s what the case uses to deliver its additional power surge.

A button on the back of the unit allows you to apply the charge if it hasn’t happened automatically and a handy four-bar gauge lets you know if the case itself needs to be rejuiced.

Be under no illusions this does turn your iPhone into a solid piece of kit and you’ll be aware it’s there in your pocket. If you’re style conscious and not going to be away from a charging point for too long, the PwrVault slips off easily to be replaced by something better looking. However, this baby is all about usability and if you’re tired of seeing that ’20 per cent power left’ warning message, this can help you push way beyond the usual limit.

Verdict: 8/10

ipowerup iphone 4s pwrvault side