Why my Jbl Boombox is not fully charging?

My JBL Boombox is experiencing charging issues (already updated to latest version). It seems that when the battery level is low, the device displays a red light, but when i plug in the charger, it quickly jumps to four white lights and blinks normally. However, after approximately 20 minutes, the charging stops. When i plug it in again, it doesn't indicate a full charge but rather shows four LED lights with one continuously blinking. It never shows full charge even if i do the same plugging an unplugging continuously for 5 hours. Seems like it takes several breaks while charging. Can someone help me resolve this issue. Thank you