Do Hybrids Hate Hot Weather?
 

More specifically, it hit 105F+ in Greater Boston, MA today. I noticed that my regenerative brakes didn't go nearly as "deep" into the blue regeneration zone as they usually do, and even coming down from 60MPH it only dipped halfway. Then the conventional brakes kicked in.

Never seen this before--the RB performed normally on the first two "serious" applications (high speed regen down to slow, ~20MPH), after that they seem to "fade."

First a disclaimer: There are experts here who know exactly how things work (I only have observations to contribute at this point). :)

I noticed the same with mine (different system, but similar physical properties). The IMA System was called-upon less frequently, more engine RPM was required through the CVT, and I heard the pack's rear cooling fan for the first time. It had been parked outdoors on a 100+ degree day and the vehicle just labored the entire 45-minute, 50/50 city/highway route (and continued to do so every afternoon during the hottest days, which have been many).

A big hit in FE was noted and the battery depleted faster on a well-tested route, with same traffic conditions / driving style, similar wind, with the variable of being hotter and more humid. I think the temperature may effect the way the pack can handle rapid charging through regen braking (which equals heat) and likely feels like fading, requiring more pedal/hydraulics.

The cooling fan took me by surprise -- it was based on whether I had the HVAC system on, so it may use part of the A/C or blower(???). I noticed it while backing in the garage and powered-down the A/C as usual to get ready for next startup (just being curious, I switched the air back on and the pack cooler was noticeably loud -- earlier, I didn't hear it over music, traffic, etc). I make it a habit to keep the vent completely uncovered by the seat belt and direct some cool air back there.

Lately, I have parked the Insight, and have used the Integra when I don't need the child seat. I have a nagging concern that the batt pack wears faster in these conditions. Again, just a conjecture...

RH77

There are thermometers inside the battery pack to keep an eye on the temperatures. If the pack got too hot it will limit the usage of it I'm sure. The general rule is batteries are pretty much like people, they like the same temperatures. If its too hot for you, its too hot for them (same goes for cold). Using your A/C is a good idea to keep them happy and give them a long life. While talking with a guy who rebuilds battery packs for hybrids, he said the #1 cause of failure is overheating.

My AC was on the whole time @ 78 or less. So I'll just keep it that way.

I've had just the opposite experience. Although there are times when the battery seems to be temperature-limited, overall I get much better mpg in warm to moderately hot weather. Luckily I seldom have to drive in really hot conditions, though: mid-90s are usual max, and more often high 70s to mid 80s.

I haven't seen markedly decreased performance in upper 80s/mid-90s. But past 100 is where the issue arose for me.

I would think that the use of A/C is the reason for this? Though if the battery does get too warm, then there is a fan in the pack that runs to cool it, I think?