Original Apple type 1 battery for the PowerBook Duo range. The type 1, 2 and 3 batteries are physically interchangeable but the type 1 had a battery status slider (passive just to note whether charged or not) and the type 2 and 3 did not but had higher capacity.
Note that due to the age of these machines, the original batteries will not hold any significant charge and are sold for display purposes only.