Confirmed, replicated the issue, found the root cause and the workaround. Atleast for me... The ball is in Opera's team to decide if its actually an issue or not.
Its the battery saver mode in Opera which gets invoked when charger is not connected. It restricts some of the Opera's functionality in some or the other way. The only info I had was Battery saver works by blocking javascript that may look malicious and barring ads which may take their own processing.
I didnt know it can fiddle with Youtube video quality too. In case this is an issue, Opera can look into it or maybe whitelist it or create some sort of exception. In case its not an issue but rather a functionality, user should get some sort of message or one time message so he can know what Battery saver can do in nut shell...
