SONY MD MZ-1 BP-MZ-1 battery adapter

This adapter can let you use 18650 battery to replace original DB-MZ1 Ni-Cd battery

You also need to soldering a metal plate on "+" side to reduce distance of battery pin

because original original BP-MZ1 battery pin are more close

And you can paste a piece of conductive gasket in bottom of the battery adapter or if you can not get conductive gasket you also can soldering it with wile to make battery in series (7.4v)