Freefly Superlight batteries use the Pixhawk Battery Interface, an open standard the we helped create! Freefly SL Series Interface Standard is linked here and should be used by anyone who wants to integrate the SL batteries into your own hardware solution.
For mechanical integration, here are the CAD files: SL8 and SL4
If you have any questions on this specification, please let us know.
Do not connect in series. For example, do not connect two 22 volt batteries together to make a 44 volt supply.