Square dance speaker external 7.4v battery

The internal battery pack is 18650 battery pack in series, the output voltage is 7.4V, but the charging voltage is generally used 9V to 12V. So, the external battery pack has 7.4V, but the battery does not have 7.4V. You can use two electronic scale battery 4V in series can also be used directly with 12 battery instead.