48-11-1820 M18 2.0 Ah battery
The 48-11-1820 is 18 volt battery pack with a capacity of 2.0 Ampere hour for the Milwaukee M18 battery system.
Inside this battery pack are five 18650 Lithium Ion cells and battery management electronics to prevent damage to the cells by overheating.
Milwaukee calls this a CP battery which stands for "compact" because it contains five cells and is smaller and lighter than battery packs that contain ten cells.
Exterior
The battery pack has a black plastic rectangular housing. On the top at the front is a battery charge indicator with four red LEDs and a push button to activate it.
On the sides are two red push buttons that need to be pushed in to release the battery when it is inserted in a tool or charger.
The electrical contacts are on top, recessed near the back.