Nikon D5000 Battery Life

Nikon provides two sets of battery life figures for Nikon D5000, one based on the CIPA standard, and the other on their in-house, Nikon standard.

Only a single power supply condition is tested:

One fully-charged Nikon EN-EL9a in-camera.

Single-frame release mode, CIPA standard
Figures calculated based on CIPA (Camera & Imaging Products Association) testing standards (see the section titled "Standard Procedure for Measuring Digital Still Camera Battery Consumption" for more information) are obtained in the following manner (quoted from the Nikon D5000 Manual):

Measured at 23°C / 73.4°F (±2°C/3.6°F) with an AF-S DX NIKKOR 18–55mm f/3.5–5.6G VR lens under the following test conditions: lens cycled from infinity to minimum range and one photograph taken at default settings once every 30 s; after photograph is taken, monitor is turned on for 4 s; tester waits for exposure meters to turn off after monitor is turned off; flash fired at full power once every other shot. Live view not used.

Nikon D5000 battery life, CIPA standard:

One EN-EL9a battery (in the camera): Approximately 510 shots

Continuous release mode, Nikon standard
Figures calculated based on the Nikon standard are obtained in the following manner (quoted from the Nikon D5000 Manual):

Measured at 20°C / 68°F with an AF-S DX NIKKOR 18–55mmf/3.5–5.6G VR lens under the following test conditions: vibration reduction off, continuous release mode, focus mode set to AF-C, image quality set to JPEG basic, image size set to M (medium), white balance set to v, ISO sensitivity set to ISO 100, shutter speed 1/250 s, focus cycled from infinity to minimum range three times after shutter-release button has been pressed halfway for 3 s; six shots are then taken in succession and monitor turned on for 4 s and then turned off; cycle repeated once exposure meters have turned off.

Nikon D5000 battery life, Nikon standard:

One EN-EL9a battery (in the camera): Approximately 2900 shots

Unlike Canon, unfortunately, Nikon does not provide separate battery life figures for movie and Live View shooting, and photography at 0°C / 32°F / freezing temperature.

Other Battery Life Factors
In the D5000 Manual, Nikon advised that the following will lead to a reduction in battery life and number of shots:

Using the LCD monitor.
The shutter-release button is kept pressed halfway.
Autofocus operation is repeatedly performed.
Shooting NEF (RAW) instead of JPEG images.
Slow shutter speeds.
Using the GP-1 GPS unit.
VR (vibration reduction) mode on VR lenses is activated.

Some lenses draw more power from the camera's battery during operation due to their physical (heavy lens elements that need more power to move) and electronic (type and technology of the VR employed) properties.