Bought my Prius in April, now seeing the effect of cooler temperatures during fall here in New England. Interestingly, we've noticed that the battery SOC is trending up as the weather cools. The battery has been almost always at 1 bar less than full for the past month. Is this typical for fall/winter? I would think that this trend would contribute to lower mpg due to less assistance from battery, making the cooler weather drop in mpg worse.
Hi MIE, Yep, that is what the Prius does. The car will keep the SOC higher in cooler temps. The main cold weather drop in mileage is cold tires, bearings and bringing the engine up to temp, only to shut the car off shortly thereafter.... It actually helps out with Pulse and Glide mileage. As your not flirting with 2 bars so often....
The -main- cause of the traction battery SOC rising is you begin to use the heater. If the coolant temp is below about 64C the engine will run (it's then a gasoline heater ). It takes quite a while to get a Prius to warm up the coolant above 70C - I find on the GII it needs DRIVING (above 60 km/hr or 40 MPH) for 5 min or so. If you are in the city, this can be hard, due to lights etc. In that case 15 min of city driving. Anyway, because the engine is running more often, there is more charge generated and put into the traction battery so the SOC tends to run higher.
"ECO" Same here. This morning we had our real first snow (~25 degrees) on the ground and traffic was 55mph (normally 65-70). My SOC by the time I got to the parking garage was two bars. Lower than normal(4-6 bars). I was able to glide much more @ 55 than normal which accounted for the lower SOC. What I am getting at is I don't think you can directly associate a higher SOC with lower temps. There are so many other variables.
I expect you are correct. I was originally asking if the computer was bumping up the SOC intentionally as it senses lower outside temps, but the previous explanation that the engine is running more at cooler temperatures is probably the right answer, leading often to a higher SOC, but not necessarily always as you point out.
Lower temperatures are not necessary for a higher SOC, but they are sufficient. The increased operation of the ICE for heat often produces a high SOC in my Gen II Prius. Tom
