Hey Trashman, many of the early Sigmas didn’t use batteries, they used backup capacitors.
You can replace them with are rechargeable battery, nicad or Nimh. Or you can order backup capacitors. I used a 1/2 AA in mine and it worked fine. You just want to remember that you need to power on the game every few months if you aren’t using it a lot.
I think there are instructions on NLG if you want to put a non rechargeable battery, you remove a diode or something like that, you have to stop the charge current from going to the battery. For me it was just easier to put a rechargeable component back in.
Chris