It battery adapter can let you use normal battery(AA or 14450) to replace old 6V lead acid battery

You also need order material as below:
Copper foil
Conductive gasket

You can use 4x1.5v AA battery，recommend to use 1.5v Li-ion battery for better operation time
or you can use 2x3.2v Li-Fe 14450 battery(the blue one in photo) + 2x dummy battery(the yellow one in photo)

Warning:Do not use 14450 Li-ion battery(3.7vx2) for this adapter,the voltage will to high to damaged you discman!