There are hundreds (if not thousands) of portable phone batteries flooding the market and it's getting harder for new ones to distinguish themselves from the pack. The Scosche GoBat backup battery costs more and weighs more than a lot of batteries with the same output, but it's specifically designed to take a ton of abuse and built with IP68 waterproof/dustproof rating and Military Spec 810G Drop/Shock construction.
That means you should be able to run over it with a truck in a muddy field and it should still be good to go.
There's a charging light, a connector for a micro USB cable to charge the battery and either one or two 2.4a USB out ports to charge your devices behind a waterproof door that's constructed well enough to stand up to heavy use. There's also a carabiner clip for hooking the battery to a backpack.
If you're tough on gear, this is the kind of battery that's going to hold up to a lot more abuse than the generic batteries they're selling at the discount mart. There's even a lifetime limited warranty. If you're spending time out in the elements, the GoBat could be the way to go.