These seem to be well received on Amazon - 4.7 out of 5 from 234 reviews.
The Marsboy Wireless Bluetooth Speaker is a little 5W speaker with a built-in 1800mAh battery that lets you play "UP TO 12 HOURS/300 SONGS PLAY TIME" from a single charge. You pair your phone to it, and you play songs.. you know the drill.
It has Bluetooth 4.0 so that means less energy usage, longer range and rapid pairing.
Available in "Milky White" and Black.