A card of two Energizer 2025 lithium coin batteries (CR2025). Lithium coin cells power small electronics such as car remotes and keyless entry fobs, bathroom and kitchen scales, glucose and heart-rate monitors, watches, calculators, garage door openers and computer motherboards. Each cell gives 3 V and measures 20 mm across and 2.5 mm thick, slightly thinner than the common 2032, so match the size printed on your old battery. The card is child-resistant and the cells contain zero mercury. Swallowed coin cells are dangerous to small children; keep spare and used batteries out of reach. Fit the cell with the positive (marked) side facing as shown in the device.