Wiesbaden

Hi, I have a 2016 370z Sport Tech. Last week went to jump in the car and drove off and realized the oil temp gauge was stuck below at 6 o'clock and the speedo was reading low- like really low going about 40mph and it read 15mph. went back to the house and jumped in my grocery getter and left for work. I took the car to Nissan (I have an extended warranty). The car currently has 27,000 mile on it. Got in it to take it to the dealership the next day and the speedo was now working, but the oil temp gauge was still in-op. At the dealership, I turned the car off in the bay and had to restart it and guess what- the oil temp gauge went back to normal at start up bouncing to top of gauge and then back to the temp it was running after driving it. The dealership said that the only codes were comm codes 1 for tranny comm. The other plain communication codes and could'nt find anything else and the gauge is now back to normal?? They checked the battery also and said battery was fine just not a good brand- cheapy. So, I drive home park it in the garage overnight and go out to start it and same thing- oil temp gauge not working and by the way the speedo had only the one incident and has been working fine. Go back to the dealership and once again I get there,shut the car off and restart it and oil gauge works. The tech thinks its the oil temp gauge going bad. Warranty will cover it, but I'm not sure I want the interior partially torn apart and my service advisor also suggested (he inferred the tech had the same opinion) to drive the car and see what happens since when I shut the car off and restart it"s fine. I was thinking of putting a good battery in it and go from there. Any thoughts of what might be going and recommendations for quality battery would be appreciated. Thanks