I've been driving/commuting in my prius for 6 years and thought nothing would surprise me. Today I was surprised. First, let me explain how i drive my prius while commuting in the suburban/city. I use a HV battery sparing/MPG maximizing technique that means that I never use EV mode, let the engine warm up some (by slowly driving that is) before leaving parking lot/entering roads, accelerate briskly at the top of Eco (sometimes more if the flow of traffic requires), and glide with no power flow (HSI near zero). With that driving, there is little discharge of the HV battery and the status of charge is near constant at the 6-7 bars [corrected from 7-8 bars]. Rarely, i get the HV battery discharged to 2 bars when "idling" with AC on. Today, I was driving the second mile of my commute, engine warm and on (accelerating from 20-40 mph at the top of Eco zone) and i noticed that the HV status of charge went down to 3 bars and possibly even 2 (I had to look at the road). Later, it recovered, especially with regen braking. Sure enough the mpg in this trip was sub par (near 50 rather than indicated 55+ i tend to get these days with AC on and non LRR tires). What"s going on? Weak HV battery? Thanks!
good question. and how to determine if the battery is changing, or if the computer decided the engine wasn't up to snuff and used more battery for some reason?
Sounds kind of like the recalibration behaviour of Honda's IMA system, which the car's computer invokes when it doesn't trust it's perception of battery charge percent. The computer vicariously keeps track of how much charge has been deposited and withdrawn, bases it's perception on this. With an ailing battery it'll find the "books" not balancing, and reacts by first showing charge as minimum, then going through a forced charge regimen, and finally declaring the best it can do as "fully charged".
I mostly try to drive similar to the "battery-sparing" way you describe. My battery state-of-charge indicator shows exactly 6 segments most of the time, never 8 except after major descents. Occasionally it inexplicably drops to 2, much as you described, then may not do that again for several months. Those drops typically seem to occur when I'm in an unfamiliar area, distracted, and not observing usual habits.
The main time I'll see 2 bars is on very flat roads at lower speeds, and extended crawl pace driving, say around a parking lot, or in a traffic jam.
LOL, i counted the bars again, and it was 6-7 (mostly 6) on the return trip. So, i really meant 6-7 and not 7-8 like i said in my initial post. I used to get full battery (it's 9 bars, right?) at the bottom of a hill after slowing to a stop. But not anymore after the inverter recall, only 8 bars.
The traction battery delivers about 200V. The cars inverter can make out of those 200V, 600V. For me this usually happens when driving slow and delicate like you. If the petrol engine is still working (warming up) and you are going slow the inverter sometimes kicks in with the 600V lowering petrol consumption but understandably increasing battery usage. Thanks to that your battery charge will drop really quick, usually to 2 bars.
no, when my engine is warming up and i drive slowly (parking lot or driveway speed), there in no measurable drop in HV bars. It would be if I started spirited driving on warming up engine, but I don't. It takes me a mile to get out from my subdivision and that takes care of the problem. However, i force the engine on by gas pedal as soon as get ready light and i live in much warmer climate than you do.
This "boost" does not happen only when warming up. To get this boost you only need to be going bellow 40 miles/h and have your petrol engine working for any reason.
