A total of 3 reviews of this product on Reddit.
I bought this for my ski. https://www.amazon.com/UE-Wireless-Bluetooth-Waterproof-Shockproof/dp/B00YARCGQA
I hang it on a zip tie on the handle bars, using the built in attachment and a back up carbineer. I’ve flipped the ski a handfull of times, no prob. You can’t hear it at full speed, but cruising and sitting at the beach it’s plenty loud enough.
No real install needed, no second battery, it’s not pretty, but very easy.
If you’re using it by a pool you should take into account the water resistance. Never used one or heard one but the Logitech UE Roll is supposed to be good for the money and fits your requirements.
This is $67 but pretty close, UE Roll bluetooth waterproof speaker. It’s crazy loud and very well made. I forgot mine in my truck bed once and it rained and was under water for a while, still works great.
I use it on my bike as well, the strap works great to put it where ever.