We've been having 100 degree days here in NYC. I've made an interesting observation and was wondering if this happens to anyone else. We have the 4wd.
Normally when I brake I get regeneration into the blue zone on the power meter. Recently, I noticed that I will only get that first thing in the morning and only for a limited time. The car will only regenerate in the dashes when it heats up. I haven't tried the highway in the heat (maybe the increased airflow will cool down the system). This only happens in 94+ heat. I guess another reason for poor FE in the heat.

I've read that hybrids get hurt by A/C more than non-hybrids. If in the heat you are running A/C, the A/C probably "captures" some of the regen energy thereby reducing the regen that can be captured for the batteries. It may be less the heat and more the A/C that's responsible for the difference you see. One more thing-traditional car batteries are less effective in high heat (in addition to extreme cold) - so maybe there's some thermal reason the battery can't receive as much energy as under hood temps increase (like in 94+ temps)?

2001 Classic Red Mazda Miata (+/- 30MPG)
1998 Toyota Sienna (+/- 23MPG)

In addition, there's also the issue of battery longevity. When it charges, it gets warm, if it gets too hot, there's problems. When the battery is already hot, and you charge it, there's probably the same safety protocols that other hybrids have that cut off charging to allow the battery to cool a bit back to safe temperatures before charging again.

First 4WD Hypermiler

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