To change the Ensoniq SQ-2's battery, first take off the keyboard's bottom cover, seen here.

Remove ALL the bottom screws except those that attach the feet.

Once the cover is removed, you'll see the Main Printed Circuit Board, which holds the backup battery.

We need to flip over this board so we can de-solder the battery from the underside.

The first step is to unplug two connectors from the Main board.

Gently rock the two, multi-pin connectors, seen here, off of their matching header pins.

Notice that the backup battery is near the 10-pin connector.

Next, remove five hex nuts from the rear panel jacks seen here.

A 9/16" hex nut driver is helpful.

Then, remove one screw (right) from the rear panel.  It attaches to a PCB mounting brace.