Lost part under battery connector, is it important?

I have an old iPhone 4 that I'm going to sell, but before i sell it, I lost a part so I want to know if it's okay to sell...

I lost the little black thing underneath where the battery connects to the mother board. This phone is unlocked and is not planned to be used for calling.

I have had to replace the battery for the phone many times so I want to know if that's the problem, if so, where can I buy another little black thing.