Hybrid Traction Battery in extreme heat

Are you using air conditioning? I see that you're driving 2012 US Prius so it may behave a bit different (US models tends to use battery less than EU models as I can see on this forum) than mine 2011 EU version.

Prius will take care of extreme conditions itself. When battery is very cold (below freezing) it will avoid using it at all (event at S0 warm-up stage) until it heats up a bit (by gently charging/discharging). I often see 7 bars in winter during warm-up period.

1. When it's hot (battery runs over 40 deg. Celsius) car also does what it can to cool battery down.
First you have to remember that the battery will run as hot as car cabin is. If you switch A/C to comfortable levels fan and air vent in rear seat will cool down battery too.
2. A/C compressor in Prius is powered directly from the hybrid battery. It can "eat" all usable charge within 15 minutes running at full power (which takes place on a very hot day with hot interior/plastics that release heat to the car). Even if you drive with ICE ON much of the power goes to the A/C compressor rather than to the battery.
3. Next thing is that hot battery can not accept high power current while is hot. It would heat it up more probably damaging battery and even making it catch fire. So logic in the car uses it only as low and easy as possible.

I'm pretty sure that if someone would try to push Prius to the limits in very hot weather it's real power would suddenly drop down to 100 HP generated solely by petrol engine with almost no assist from battery and MG1/MG2 pair working only to give better torque on lower speeds and eCVT.

On the very hot day this summer I've seen no more than 4 bars on my battery, while A/C fan (auto) never dropped below 4 bars of speed (internal temp. set 8 degs below external temp. 37 deg. C). ICE turned off only during full stop and even 10 KM (6 mi) spans never get battery fully loaded. While staying on traffic lights for 2-3 minutes cycle the battery often dropped by 2 bars. And when you hit 2 bars you get forced recharge until 4 bars which may take ages in that conditions.
This day consumption skyrocketed to 7.5 l/100km on average, over 2 l/100km more than typical city result (for this specific car/use scenario).

 

Don't worry about it. The car will take care of the battery. That's what it's programmed to do. Just make sure the battery vent (rear seat) is not covered by anything (watch that seat belt!) and do use A/C, as the car uses the interior cooled air to cool the battery.

 

I agree with all the above posts. This is mines 3rd summer and I've come to accept lower MPGs when it's really hot and I make short commutes. The ICE runs more to charge the battery when the AC is operating since there is a drain on both batteries. I've come to accept that the SOC will often read at just 2 bars during extreme heat. Like David says...the on-board computers will handle everything. Lower mileage is a reality for all cars during extreme heat.

 

I used to hypermile, but my results were not as great as some members on PC. Plus, if you drive in the Phoenix metro area, you tend to get aggressively passed by the "guzzlers" here, which are rampant. I've come to accept lower than 50 mpg city driving and just keep up with traffic now. I'm satisfied with 45 to 48 mpg depending on some freeway driving and outside temps. If I'm on a trip and the wind is to my back, I've pulled off 48 to 50 mpg on the road. I used to try ECO mode, and for a thrill, tried PWR mode too...I'm pretty much settled in on normal mode and just drive carefully but not so much as to cause everyone to pass me.

 

As long as the Prius is running - its HV battery thermal management system will keep the battery from getting too hot. When the Prius is parked and turned off - I believe the HV battery thermal management system is turned off and it then that the Prius HV battery is most often at risk of overheating. Park the Prius in the shade if you can.

hope this helps

Walter Lee

 

thanks for all the comments, this is a great forum. I'm having same issues with my CHR. And I cannot understand how Toyota doesn't use active thermal management on the hybrid cars. It's really frustrating for us living in very hot climates.

 

welcome!
too expensive, i suppose. they won't admit to it though. in reality, you do have active thermal management. it's just of a low quality.