Won't play without being plugged in

My UE Megaboom will only play when it’s plugged in.

It will flash like it is charging for around a minute then the light will go out and nothing happens. If I turn it on while plugged in, it will turn itself off after around 10 seconds unless I am running something through it. I have tried resetting and replacing the battery with the same results. The speakers crackle at high volumes but I am sure this issue is unrelated.

It would be a shame to throw this thing away because they are great when working properly.

The only thing I can think is that it is not charging because initially it was turning off and on every few seconds but now I also get the critical battery warning if I don’t play something through it. So the power must be getting through.

Any ideas????

thanks