Two rechargeable D cell batteries.
Specifications:
Classification: Rechargeable
Chemical System: Nickel-Metal Hydride (NiMH)
Designation: ANSI-1.2H4
Nominal Voltage: 1.2 Volts
Rated Capacity: 2500 mAh* at 21°C (70°F)
Typical Weight: 73.0 grams (2.6 oz.)
Typical Volume: 57.0 cubic centimeters (3.5 cubic inch)
Terminals: Flat Contact
Jacket: Plastic
* Based on 500 mA (0.2C rate) continuous discharge to 1.0 volts.