The battery shouldn't have any effect on whether the display on the console works.
The function of the battery is to keep power to the bios chip, and thus keeping the settings when you turn off the power.
If the battery is dying, the bios settings will be reset.
The most important settings in the bios, are the settings for the serial com ports, and the midi card.
That's why there might be communication problems, if the bios settings isn't set up right.
Since these are old machines, that's why we tend to recommend that people change to a fresh battery.