All,
Yes, search for "UB1250" in google and you'll find online retailers for this. You need two of them (yes, the same batteries are used in the Sig 30 as the Sig 70s.. .and the .2 models).
When you receive them, I recommend that you voltage test them before you install them. IMO, the voltage should be at least 12.6V... otherwise, the battery was sitting on the shelf too long without enough charge and it might not last as long as it should.
Also, the battery voltage of each battery should be close (ideally within 0.1V of each other).
Next, make sure you FULLY CHARGE the new batteries after you install them, and BEFORE you use the unit.
I think I've run mine down on my Sig70s one too many times and they need replacement.
You are a perfect SMART board candidate

Best regards,
Vinnie