Nikon has released a firmware update for its D40 and D40x DSLRs. Firmware version 1.12 for the D40 and version 1.01 for the D40x will improve the function of the cameras with Nikon's EN-EL9a batteries.
Before this firmware update, the EN-EL9a batteries were shooting less photos than the original EN-EL9 pack; however, this firmware update will fix the compatibility problem. The CIPA standard tests report that the D40 should be able to take about 510 shots in single-frame shooting mode with the new EN-EL9a firmware. This is an improvement from the 470 shots available with the original EN-EL9 battery pack. In continuous mode, the EN-EL9a battery pack should shoot about 2,400 shots according to Nikon's tests.
The new firmware is available from Nikon's support web site.