Korg DDD1 Battery

I am trying to find a replacement battery which is a Sanyo CADNICA Model 4 N-270AA
This is a 4.8V 270 mAh battery.

That does not sound like the correct battery. The DDD-1 uses a 3V lithium battery:
Battery, 3V lithium - Syntaur

I double-checked the service manual, just to be sure.