These days, you can buy a USB battery pack from just about every manufacturer. We've reviewed several, and they're uncomplicated gadgets: you charge them up, then stow in your bag / glove compartment / pocket until one of your other gadgets needs an emergency top-up.
They differ mainly in capacity, and Go Baby Mobile's Power Pack has a 10,000mAh cell - bigger than most USB batteries. This also makes it physically bigger than most, including Innergie's PocketCell.
Another difference is that the Power Pack has two USB outputs, so you can charge two devices at once. The top output delivers 5V at 2.1A, ideal for power-hungry tablets such as the iPad. The bottom USB port produces 5V at 1A, and is the one you'd use to charge a smartphone, or other less-demanding gadget.
Stylish it isn't, but you're unlikely to buy such a device based on looks. The white model looks better than the black, and both have four blue LEDs which tell you the remaining capacity. These also flash when charging so you can tell when it's charged.
Bundled with the Power Pack are multiple tips including mini USB, micro USB, Apple 30-pin, Nokia, Blackberry and Samsung adapters.
Go baby mobile claims that the Power Pack can recharge an iPhone up to six times from empty, most tablets up to two times, and will recharge in 3-4 hours.
In our tests, we found that the battery could charge an empty iPad 4 up to 60 percent (using the 2.1A output), and took four hours to do so. Alternatively, it was able to charge an empty iPhone 5 completely (using the 1A port), with enough juice left to charge a run-down iPad 4 to almost 40 percent.
Recharging the battery using an iPhone mains charger (it supports charging at a maximum of 1A) took just over five hours, and around double this from a PC's USB port. At least it uses a standard mini USB connector to charge unlike the awkward PowerMonkey Discovery.
Although it doesn't quite live up to the claims, the £40 price makes the Power Pack good value. It's convenient being able to charge two devices at once, and its power reserves are also impressive given the price - certainly beating any other USB battery we've tested.