My ford explorer 2017 says "charging system service now" what does it mean?

What is your question?

The car was parked outside under the harsh winter and some snow entered under the bonnet. We wanted to start it and used a battery booster to start it, it came on once, but when we removed the booster, the car went off. We reconnected the booster and it started again, but we noticed it displayed - "charging system service now". The car is almost new. what could be the problem?