I’ve been using Lithium Li-on batteries in various scooters for the past 6 to 7 years and my scooter is always left in the car, hot or cold, outside with the car on a hard standing and never had any problems with the batteries.
In cold weather I’ve found the battery meter on the scooter shows a low voltage because the battery is cold but within a few minutes of getting under way I find it soon perks up to show almost but not quiet, full battery level, much the same that I used to get with GEL batteries of years gone by.
My Lithium battery in my current scooter is getting on to be 7 years old now and has only lost about 10% of its original capacity.