I recently got a passthrough, but have had a battery pack for charging my batts for much longer.
Whilt it works perfectly charging the batteries, I was very disappointed that the pack did not power my passthrough.
We were discussing this on another forum and someone discovered with theirs that the battery pack DID work with the passthrough...... providing you didn't press the button and turn the battery pack on!
So, battery pack now works great with the passthrough!
Someone else (with a different type of pack) also found the same thing with theirs.
Incidentally, the pack output is 700mA