The wires can move, the video is showing that you do not want the wire to bend back and forth at the connectors at a hard angle.
Just as in any wire connection, the wires will break if you do that too much
I mount my batteries 3 ways
In a back pack if it's on my helmet
Inside a chooped up water bottle and then in the water bottle cage
Inside a pouch that is velcro'd to the top frame tube
This page has some pics and info
http://www.el34world.com/Misc/bike/BatteryPackMounting.htm