JBL S400BT Suddenly Stopped

i have jbl s400bt. One day I put it in charge and and i left it there. After then i tried the open jbl but its not responding. Not glowing and not beeping. I can use with cable but i hate cables. For me without bt jbl as such useless. I tried the teardown but no screw and looking very hard to open. So what can i do ? Its hard to say but is my problem about mainboard or looks like a just battery problem ? Sorry for my bad English. Thank u!!