If keyfob battery is low you can always take out key from it for entry, Question 1) Will car start if battery on keyfob is dead?The car has to recognize keyfob is present right?? I have keyfobs on both my Harleys I change batteries every 2 years just to be safe. Online it says for some cars? Put foot on brake as usual then push Start Button with Keyfob this is designed to override dead battery i .Hopefully works for Nissan..
Presumably these work like proximity keys for other cars that have been used for years... The similar key on both Prius cars we have, once you're in the car and have turned the car on, gives a warning on the display screen in the car that the battery is getting low. It does this well in advance of the battery actually going dead.