This is a 1.2 volt "C" size NiMH (nickel-metal hydride) rechargeable battery, with a capacity of 2800 milliampere-hours (mAh).
It is used in Nicro's Day/Night Solar Cell Vents - which run 24 hours/day on this battery, and are re-charged during the day by the integral solar panel on top of the vent.