Looks like it's going to be another week of over 90f days. How hot is too hot in regards to battery function/life? I'm lucky that I can park my bike inside while I'm at work, but will a 20 minute ride home in the heat at 4pm up a few big hills cause any problems? I don't mind being hot, I just soak my shirt in cold water before I leave, I just don't want to ruin my new bike.
I wouldn't worry about it. I've been out on 90min rides in heat in the 80s and 90s. It's not so bad with the wind blowing over you as you zoom around with your Rad. Maybe give your battery a break for 30min before starting to charge it back up is what I will typically do.
I have a 2020 RadMini 4 that's just a little over a year old. Last year I probably did at least five ~20 mile rides at 90+°F, with one 51 miler (never again!). As far as I can tell the capacity of my Rad OEM battery hasn't diminished, but it's only been a year. The battery never felt overly hot after those trips (I wish I had checked it with the IR thermometer), but after all, they were mostly in Mode 1 assist level. If you're running at higher assist levels, a battery cool down period of a couple of hours might be in order.
When pushing for maximum range last year on a relatively flat canal trail with the just off the charger 100% charged Rad OEM battery I got 55.5 miles (in Mode 1 for 95+% of the time).
This year I pushed it to 63.5 miles under similar conditions, again Mode 1 for 95+% of the time.
While neither of those trips were at 90+°F, I think they show that last years hot trips didn't kill my battery (at least not blatantly obviously).
Also, despite the warnings, OCCASIONAL instances of fully depleting my Rad battery have not destroyed or even harmed it in any measurable way so far, but I do recharge it to at least 80% IMMEDIATELY after getting home.