How do you know if your battery is degrading? Will it charge up to fewer and fewer miles?
Yes. As a battery ages/degrades, its capacity (the amount of work it can do) is reduced. Capacity is best measured in electric terms (amps, kws) not the estimated EV miles on the guess-o-meter which also uses efficiency (how you drive) in its calculations.
I have a LiOn powered worklight that when new lasted for hours; years later it’s now only lasting a few minutes on its brightest power setting. Eventually it will only last a few seconds, then no power at all. I can choose to either re-cell it with new cells or get a new one. (Sadly in our modern disposable society, it’s the usually cheaper/easier to do the latter)
HEV/PHEV/BEV owners will do the same....... eventually. I had a 2006 Prius and faced this. I chose to get a new pack and it was wonderful making the car drive like new again with full power, restored fuel economy, and reliability. Everyone that’s done it has the same experience. The car retained more value and I had zero issues selling it a couple of years later to a savvy and happy buyer.
On the garage heat issue, I’ve learned to hold off charging as long as possible to let the pack cool down. Then charge right before heading out the next morning (charge window: 3am-6am) so it doesn’t sit for long periods fully charged. Obviously, L2 charge rates apply. During the hot months, I also skip any opportunity fast charging outside during the day and use HV if need be.
YMMV