Hello!

Went out to fly yesterday but after 2 batteries the controller rapidly heated up to the point a had to switch it off. The controller was unpleasant to hold and had that overheated plastic smell to it.
During the last flight the controller disconnected from the spark a couple of times (max 5m from the controller). Running the latest FW (21/8).

Best Regards

Kalle

It is abnormal to have overheated plastic smell to it, I would recommend you send it in for diagnosis, please refer to the link below to contact the Support to start a case. Besides, please provide me with your case number once you got it, I'll keep an eye on it.
http://www.dji.com/support