EY9L53 18V 3.0 Ah battery
The EY9L53 is Lithium Ion battery pack for the 18 volt battery system from Panasonic.
The battery has a nominal voltage of 18 volts with a capacity of 3.0 Ah. Inside the battery pack are five Lithium Ion cells with a capacity of 3.0 Ah each.
Availability
The EY9L53 seems to have been replaced with the EY9L53B which has a similar exterior and specifications. See that page for more information about this battery.