Depending on your needs, another great portable sound system is :

http://www.amazon.com/ION-Block-Rocker-Bluetooth-Auxiliary/dp/B007WCJVH2

It's been around for a while. AFAIK you can order them from Costco.

Some users gave bad bluetooth reviews, but in most situations it's fine (at 10ft+ it can be sketchy depending on the device).

It doesn't take batteries, instead it's charged. Also the volume caps out very high, so in the forest setting you'll only ever need ~%50.

Also, you can charge phones/electronics through USB on it. It has an AUX cord too, if you don't have a bluetooth device.

I've seen them routinely run for 30-40 hours without a charge at 50% or below volume and no phones charging off of it.

If you're going to be using speakers for 8+ hours a day every day at forest, battery operated will serve you better. If you spend a lot of time in the forest (go in early/stay late), this is probably great.

Here is an amazon link to the speaker I brought to our last tournament. Solid, decently loud, great sound, pretty portable (it comes to a little below shin-height and has wheels and a handle), Bluetooth and AUX inputs, and a fantastic battery life. Only thing is I don't believe it's water resistant like /u/Cbcasey's suggestion. Amazon also has it refurbished for $120.