My UE Megaboom after months of not using would show as charging for about 10 Seconds with white flashing light. Then light went out and wouldn’t charge after 10 seconds. If I turned on, it said critical battery please charge. After several attempts of removing power lead and reconnecting still same.
Decided to open UE app and it allowed me to connect to speaker. Clicked on the power icon on app and Speaker woke up and immediately started charging and carried on charging. Weird but it worked.