When replacing batteries in a Bally early solid state machine, you can use 3
regular AA batteries instead of rechargeable batteries. To do so you will
need to install a diode so that the machine doesn't attempt to charge the
batteries while the game is on. The diode should be on the positive
connection between the batteries and the board. The diode should have the
banded end of the diode towards the board. This whole setup is assuming you
have installed a separate battery holder off the MPU board in place of the
original rechargeable battery.