Goal Zero Rock Out 2 Portable Speaker, Blue Dark Bass technology; innovative chamber delivers precise, high-quality sound every time Rugged, water-resistant shell protects the speaker and your gear Juice up the internal lithium battery in 3 hours from USB or sun Chainable with other Rock Out version 1 or Rock Out 2 speakers for more sound Versatile bungee cord allows for securing the speaker on your ride, belt loop, backpack, etc