New Nikon support article: the Nikon EN-EL14a rechargeable Li-ion battery can now be used in place of the EN-EL14 battery (both batteries are priced at $49.95). Some cameras may need a firmware update in order to work with both battery types. Keep in mind that the latest firmware updates will most likely make third party batteries incompatible with your camera.
Here is the full text of the article:
The EN-EL14a rechargeable Li-ion battery can be used in place of the EN-EL14 rechargeable Li-ion battery.
The EN-EL14a battery life has been improved by up to 20% compared to an EN-EL14 battery (depending on the camera model and shooting conditions). Both batteries can be charged using the MH-24 battery charger.
All cameras that currently use the EN-EL14 can also be used with the EN-EL14a. See the following for further information regarding EN-EL14a compatibility with each camera.
D5200, D5100, D3200, D3100, COOLPIX P7700- By upgrading firmware, EN-EL14a performance is maximized and more images can be captured (battery performance) when an EN-EL14a is used than when an EN-EL14 is used.
D5200 - Firmware C: 1.01 or later
D3200 - Firmware C: 1.02 or later
D5100 - Firmware A: 1.02/ B: 1.01 or later
D3100 - Firmware A :1.02/ B 1.01 or later
COOLPIX P7700 - Firmware version 1.3 or later
COOLPIX P7000 or P7100 - Although firmware enabling support for the EN-EL14a will not be released, the battery can be used with these cameras. However, the camera's battery indicator may quickly reach the half-charge point on its display.
COOLPIX P7800 - The camera already supports the EN-EL14a from the time it was initially released, so does not require a firmware update.
Nikon Df, D5300, D3300 - An EN-EL14a is included with purchase. The EN-EL14 can also be used with these cameras.