2 
1 I replace the battery and sound more when is plugged to the power
i replace the OEM battery because it was bad now i have new batteries but when is plugged to the power sounds more powerfull like more bass and When i disconect from the power is less powerfull, not like the original ones . Any suggestion??
i used 4 Panasonic NCR18650B Super Max 3.7V 3400mAh Rechargeable Li-ion Battery-Green
