Yes, you can use the new Li-ion 2,900 mAh battery pack on previous model cameras:
H2D, H3D, H3DII, H4D and H4x.
Hasselblad USA website:
http://www.hasselbladusa.com/service--support/technical-support/firmware-downloads.aspx
Camera Body firmware: H4D, H3DII, H3D, H2D 2.3.1/16.0.7
Firmware version 2.3.1/16.0.7 is a feature release
Firmware package CB130308.hbf requires one of the above mentioned Hasselblad digital capture products.
Highlights
Support for New 7.2V/2900 mAh Li-ion rechargeable battery
The firmware package CB130308.hbf for the H-series camera body, contains the following firmware versions:
Product Firmware Version
H4D 2.3.1/16.0.7
H3DII, H3D, H2D 2.3.1
Camera Body firmware: H4X 2.3.1/16.0.7
Firmware version 2.3.1/16.0.7 is a feature release
Firmware package H4X130308.hbf is for the Hasselblad H4X camera body only.
Highlights
Support for New 7.2V/2900 mAh Li-ion rechargeable battery
The firmware package H4X130308.hbf for the H4X camera body, contains the following firmware versions:
Product Firmware Version
H4X 2.3.1/16.0.7
This firmware update is only possible via Phocus. We recommend to always use the latest version of Phocus (currently 2.7.1) to perform the firmware update.
To perform this camera body upgrade you must attach a Hasselblad digital back to the H4X body. (compatible digital backs include CF & CFH). The upgrade can also be performed using a H2D, H3D, H3D-II or H4D sensor unit. In this case a message “Back not compatible” will appear but the upgrade function will still work.