Question: To hold batteries in place when the  "door" is missing.
Options:
Use scissors or a box cutter to cut a piece of cardboard to hold the batteries in place, then use  duct tape to hold down the cardboard on the batteries.
Use scissors or a box cutter to cut a piece of cardboard to hold the batteries in place, then use  duct tape to separate the cardboard from the batteries.
Answer: Use scissors or a box cutter to cut a piece of cardboard to hold the batteries in place, then use  duct tape to hold down the cardboard on the batteries.