You can now buy Nexus One batteries directly from Google. Check out their sales pitch:

Choosing Nexus One: Additional Batteries
One of the great things about the Nexus One is that you can easily remove and replace the battery. If you would like to be able to carry a fully charged spare battery, we recommend official Nexus One batteries for performance and reliability.
Please note that there is a purchase limit of five batteries per customer.
Technical specifications:
Removable 1400 mAH battery
Charges at 480mA when installed in Nexus One phone connected to USB, at 980mA when installed in phone connected to charger
Talk time: Up to 10 hours on 2G, Up to 7 hours on 3G
Standby time: Up to 290 hours on 2G, Up to 250 hours on 3G
Internet use: Up to 5 hours on 3G, Up to 6.5 hours on Wi-Fi
Video playback: Up to 7 hours
Audio playback: Up to 20 hours
Instructions for installing a battery are available from the Nexus One User’s Guide.
Note: Package includes battery only; does not include charger. Battery charges only when inserted in Nexus One phone that is connected to USB or phone charger.

Google is charging $25 for the battery.

Source: Phandroid.

3G, Batteries, Battery, Battery charger, Google, Nexus One, Universal Serial Bus, Wi-Fi