Nikon support will never answer questions about non-user replaceable parts. They will only give repair info to authorized repair facilities.
Besides, you asked them the wrong question. The 4300 does not have a backup battery. What you see in the top picture is a
memory backup capacitor. Similar to the one below:
You'll have to check the repair manual to see if the capacitor specs are listed (voltage/capacity), or open the camera and see if there are any markings.