Batteries included, but how can you tell if it’s dying?

A few weeks ago we bought a cute little waterproof bluetooth speaker so we could listen to music in the shower or while doing dishes or wherever without using headphones or dealing with crappy phone speakers.  Good purchase!  It sounds good, it’s cute and little (as mentioned above), and it’s called the Oontz Angle.  Worth it for the amusement I get out of the name alone.  Its battery is rechargeable via USB, and it’s all-around wonderful except for one minor thing: there’s no battery life indicator.

When it arrived, we couldn’t tell if it had been charged.  Most electronics need to be charged before their first use, but when we turned it on, it worked immediately.  And with almost daily use (not more than an hour a day, but still), it ran for nearly six weeks before it died.  Of course, it died mid-shower (my shower, naturally), and I had no warning.  If I’d known it was low, I would have plugged the poor thing in.  Maybe a warning light?  Where blinking means “Plug me in, please”?  But really, that’s the only complaint I have about it.