RECHARGEABLE BATTERY- BESTON1.2.V 3000MAH

That is a Sub-C (SC) Nickel-Metal Hydride (Ni-MH) rechargeable battery, commonly found in power tool battery packs or RC vehicles.
​Based on the photo, you’ve got it hooked up to an LED, but if you're planning to use this for a project or need to maintain it, here is a quick breakdown of what those specs mean and how to handle it safely.
​Battery Specifications
​Chemistry (Ni-MH): Unlike Lithium-ion, Ni-MH is generally safer and more stable, though it has a lower energy density.
​Voltage (1.2\text{V}): This is the nominal voltage. A fully charged cell will be around 1.4\text{V} to 1.45\text{V}, and it’s considered "empty" at about 1.0\text{V}.
​Capacity (3000\text{mAh}): This tells you the "fuel tank" size. In theory, it can provide 3000\text{mA} (3 Amps) for one hour.
​Form Factor (Sub-C): These are shorter and fatter than your standard AA battery