I have a 2015 Fortwo ED with low mileage. This exact same problem just started happening to me last month. For the most part, the cooling fan kicks on first and then after a while longer, the red temperature light illuminates in the cluster. So far, the car remains driveable but I’m reluctant to drive it for extended periods.
It’s been chilly here - in the 30s-40sF or cooler. Using an infrared thermometer, I’ve checked the coolant and radiator lines and even when the temperature light is on, they measure cooler than the ambient air - something like 30F when it’s 39F outside. I’m assuming the cooling fan is making the coolant colder even after driving around.
Please let me know if you determine root cause. I’m unaware of an ED shop anywhere near me so I’m on my own in trying to resolve. There is significant swirl going on in the coolant tank, so I know that pump is operating. Only things I can think is maybe a temperature sensor has failed? I’m trying to research best OBD tool to try and see if the coolant temperature is being reported and what it is.
Sign Guy - you're in Canada, it's barely spring, you're battery pack isn't going to overheat unless there is something seriously wrong with it. If there was something seriously wrong with the pack, the car wouldn't be working.