Do you mean the battery cover? I would say yes it is necessary. It will keep out dirt and hold your battery in place as well as helping protect the electronics from spills.
If necessary please give me official panel for it.
This is a fan based News and Discussion site. It is in no way run by Microsoft, Lumia or any developer. We can not give you what we do not have...
If you mean point you to where you can find one... I have no idea where you are. Try local eBay, Amazon, cell phone suppliers and Nokia Care.