Bruce hears that the lifespan of lithium ion batteries get reduced by heat. Leo says that's correct, and right now it's really hot out. That's why phones will shut down when it gets too hot. It's a safety program to protect the battery from damage. So Bruce should keep his phone out of the sun. He shouldn't let them get any hotter than normal. Even during hot days, the shade will reduce the heat by at least 10 degrees. On the other end, he'll want to avoid extreme cold as well. It does the same thing.
Image: © Raimond Spekking / , via Wikimedia Commons