Holy Moly! It's hot out there!
Anything you can do to keep the interior temperature down in your car, the happier you and your batteries will be (HV and 12V). The obvious include:
- Park in a garage.
- Park under shade
- Use a Sun Shade on your front windshield AND park facing West, so it will block the hottest sun of the day.
- Crack at least two of your windows 1/4"
- If you have the sliding cargo cover, USE IT! Protect your cargo from prying eyes AND create a dead airspace that helps insulate the battery from the heat of the sun.
The less obvious are:
- USE THE HECK OUT OF YOUR A/C!!!!!
- Don't spare it one bit. You're not putting a strain on the battery, you're saving it!
- When starting out with a hot interior, roll all 4 windows down 4" for the first 30 seconds or so - this will flush the hottest air from the interior. When it's 110°F outside, it's going to be 130-140°F inside.
- Treat it like you do the thermostat in your home - you don't run around adjusting all the registers indoors to blow in different directions - you just change the thermostat. The Prius is really no different. Aim all 4 vents up and over the shoulders of the front seat occupants. You'll get a nice breeze on both sides of their heads, and you'll circulate air nicely in the car to get the whole interior cooled - so your battery can be cooled with the cool interior air.
- The car will manage the climate way better than you can. Leave it on AUTO, recirculate, and as mentioned before, just change the thermostat up and down as needed. I leave mine on 75°F, and almost never touch it With a little patience, you will find that you barely have to touch the A/C, and you will be as cool and comfortable as the circumstances allow.
- Drive a little more conservatively. Prius drivers aren't generally heavy-footed, but some of my test drives have revealed there are NASCAR wannabees in our midst. Gentle acceleration (don't be the jackrabbit at the light, but pull away fast enough to not be a road block) along with more engine braking and less foot brake helps keep the demand low on the battery and to minimize heat.
Heat is the enemy. It's what leads to premature failure.