This is the DuraTrax Piranha 6-Cell 1900mAh NiCd Flat Battery Pack.  These are great sport battery packs, and these also great as starter batteries, offering more starts than a 1500mAh pack.

FEATURES:
New Piranha 1900mAh NiCds replace the 1800mAh packs, creating one of the best values in rechargeable R/C batteries!
Impressively higher in capacity--but priced to be surprisingly affordable.
Quality construction featueres are standard, including reinforced tubes, welded tabs and super-flex silicone wire.
Standard Tamiya-style connector.

INCLUDES: One Piranha 6-Cell, 1900mAh Assembled Flat Battery Pack.

SPECS: Number of cells: 6
Cell type: 1900 SCX
Total assembled voltage: 7.2 volts.
Batteries are assembled in flat configuration.
Connector type: Standard with 2-1/2" (14 gauge) wire.
Charge rate: 4-5 amps. Timed or peak charge.
Discharge rate: 5-15 amps.  Minimum discharge voltage: 6 volts.
Discharge average: Unknown.
Suggested usage: Sport racing.
Batteries are Unmatched.
Battery pack size:  5-1/4" (134mm) long, 1-3/4" (44mm) wide.