I have seen the various threads that suggest that a weakened 12v battery can result in lower mileage, by causing the ICE to turn on more than necessary to charge that battery. I bought a low mileage 2009 at the beginning of February, and have experienced MPG that is on the low side of the normal range. I do intermixed city and freeway driving. I had been getting 43 MPG according to the MFD, then discovered the trick about inflating the tires to 42/40 psi, and now my overall is 43.1 MPG over my initial 160 miles. One thing that leads me to suspect that the battery is weak is that when I first power on the car, it almost always starts the ICE within 10-20 seconds. In other words, even the low speed moving the car from a parking spot, which I sense should be in stealth mode, is being powered by the ICE. I have since tested the battery using the "Vehicle Signal Check" process from jdenenberg: Unloaded battery: 12.1v (supposed to be 12.4 to 12.8) Under load: 11.9v (supposed to >12v) Charging: 14.1v (supposed to be >13.6 and <14.4) These results were after the car had sat unused for three days. The first two measurements are low, the third is in the acceptable range. Since this is a 2009 model, I find it hard to believe I would need a new 12v battery. But, the measurements would seem to indicate that I do. And, maybe the car's low mileage indicates that it sat unused (which is usually not good for a battery) much of the time. Any opinions or advice? John
The ICE will always come on after getting in the READY mode when the car is cold or has been sitting for a while. It's to warm the ICE for emissions control and to provide cabin heat in cold weather. What you are experiencing is perfectly normal.
I would test the battery when it has rested overnight, rather than after 3 days. firepa63 is correct, the gen2 prius will light the ICE a few seconds after Ready Mode as part of its warmup (the gen3 will skip it if engine coolant temp >60C). For details on the warmup process, see the links in my spreadsheet here: http://priuschat.com/forums/knowled...perating-mode-availability-reference-aid.html Keep an eye on the battery, but I think you are likely fine, just need to read on P&G, etc and get some seat time with it. 50+ will come with warmer temps and more experience. Good luck!
Your symptoms arn't caused by a low battery. The prius ALWAYS starts the engine when you turn it on from a cold start. It will then warm up the catalytic converter to minimum operating temp, and then shut off.
You're probably experiencing lower than expected mileage due to low temperatures, winter gas and short trips. Summer should fix the first 2, and a nice driving holiday will fix the last one. and Welcome.
It's also possible that previous owner ran the battery down several times. It is a small battery and a couple of complete discharges will shorten it's life.
Hi John, If you have access to a battery charger, then I'd suggest you try to fully charge the battery using the 2A setting overnight. See if that makes a difference to the voltage readings when you've let several hours elapse after removing the charger. Also, what constitutes low mileage?
In the North east in the winter time, 43 MPG is normal. You should get about 47 in the spring and summer.
