A:AnswerBatteries are internal, so no, it’s not replaceable. If you bought the bestbuy warranty, like I did, bring it back before 2 years and it will be replaced.
A:AnswerYou can let it float, it works just as advertised. The quality underwater isn't the best, however you can still hear the speaker prominently. The connection worked just fine with my water tests as long as it doesn't go too deep.
A:AnswerAs long as no physical damage is done to the speaker yes it's safe in shower. I had a dog put a tooth hole threw one once and it got water damaged inside.
A:AnswerThe Wonderboom is the only speaker that does not use an app like the other UE speakers do. You will have to adjust the EQ in the music app you're using.