If it is running on a 2.4V battery it sounds as if it has been converted to PS-2 3V. Many FEF 5V boards failed. I have replaced many. He can look at the speaker to see if it is 4 ohm vice 16 ohm.
IF it was upgraded, the installed could have put in the charge port harness. Eitherway you can charge the battery with MTH charger. G