Want to make Boss RC-505 mobile with batteries, do I need a choke?
The ferrite beads aren't designed to block low frequency AC hum, but rather to reduce the amount of RFI from the device that is radiated back to the mains (e.g. from switching regulators) or noise pickup from it, and to stop the cable acting as a giant antenna.

For a battery application, you won't have those issues anyway, so in all likelihood the ferrite bead is not required.