The Dell 451-BCKC is a rechargeable spare battery for Dell notebooks, intended to replace a depleted battery in a compatible device. It gives you a portable power source for notebook use away from a fixed power connection.
This lithium-ion battery has a 3-cell design and a 51 Wh energy capacity. Its listed voltage is 14.40 V. These specifications identify this particular battery for matching with notebook hardware that supports it.