I use a Quantum 2x2 with a Quantum 5D-16 cable specifically designed to provide the correct voltage for the Aptus backs.
I've been using my batteries on an Aptus-65 for 7-8 years now. I keep 2-batteries fully charged, but 1-battery will last all day (500+ actuations).
I also cobbled together an adapter which connects directly to the battery-slot on the bottom of the back. That way, I never have to swap batteries! I just plug-into with a short jumper cable.
Good luck!
Cheers,
Hank