This is the Rupes genuine battery replacement (9HB120LT) or addition for the Rupes Nano Ibrid Polisher.
As with most things you either use often, or need to be available when you need them, a spare battery is always great to have for when your main battery runs out.
Battery For RUPES Nano Ibrid Bigfoot Polisher
Power: 10.8v 2AH
Weight: 0.26KG