I can't praise this speaker enough:

https://www.amazon.com/NYNE-Portable-Bluetooth-Subwoofer-Microphone/dp/B00I9ICWBA

It's solidly built, the sound is loud and well balanced, and it projects very well over distance. We play it in our backyard and get clean highs/mids/lows from almost 100 feet away, which is surprising for a relatively small speaker outdoors. The bass covers every low frequency you'll hear on most songs. The design is sleek. It's portable enough to carry around easily with one hand (it has a handle). The manufacturer says the battery lasts up to 10 hours between charges, though I haven't really tested that. And there's a USB port on the back if your phone needs a charge.

I was considering the Jambox, but the reviews for this were just as good for a fraction of the price- including reviews from people who have owned both. My only complaint is the Bluetooth receiver. The signal cuts out at about 20-30 feet, or if there's a large object in the way. But that's a small issue, IMO.

I've had this for a year and I'd recommend it to everyone.