Is my traction battery going bad?

In 7 years and 151K miles we've only had two tanks of gas that registered under 40 mpg. Most of the time we're hitting 42-48, averaging about 45. (If I was the only driver we would have gotten 50+ but my wife doesn't do any hypermile techniques.)

Last week we filled up and only got 36 mpg, the lowest ever. The current tank, about 200 miles of driving, is only getting 38 mpg. When we get into the car the battery level indicator shows 2 purple bars. I checked for codes but there are none.

After 7 years we know the behavior of this car and this isn't normal. We replaced the 12V battery last year. Is there anything else that could be causing this 7+ drop in mpg besides the traction battery?

If the battery is bad my plan is to buy a new one and install it myself. I understand there is a 1 year warranty on new batteries. Would installing it my self void the warranty?

 

Well my plan had been to sell the Gen II and buy a Gen IV (depending on what Toyota does to it). If I replace the traction battery I might just decide to keep driving the Gen II.

Does anybody have an idea how much Toyota would charge to diagnose the battery?

 

I will double check the tire pressure. If only it were that simple. I did just check the tire pressure (44/42) about a month ago but who knows... you could be right.

Has it been hot? We'll yes. Quite hot. But that's nothing new for this area. We live in Redding CA. Every summer we have four to eight weeks of over 100 degrees. It's not uncommon for it to be 110+. But we've lived here for four summers and the drop in mileage isn't more than 2 or 3 mpg during the summer. I do note that the air conditioner squashes about 2 mpg. We know the car quite well. While we have another car it remains parked and covered most of the time. We drive the Prius 95% of the time. We check the mileage every tank full and monitor the mileage. So a drop below 40 mpg is extremely rare.

I have read here on priuschat that hot temps apparently might shorten the traction battery life. Someone mentioned that 140-160K miles is about where hot climate batteries sometimes fail. We are right in the middle of that range with 151K miles on the car.

The other symptom is we can pull the car into the garage at the end of the day with 7 or 8 bars of charge, but have only 2 to 3 bars in the morning. That is certainly new behavior. Today we drove into Home Depot with 7 or 8 bars, but an hour later came out and had only 2 bars.

Still with all of that bad behavior no codes from the OBD.

I guess I'll take it into Toyota this week and pay them to check the battery.

 

We are seeing the quick charge/discharge to purple.

Right. No code so from what I understand Toyota won't replace it under warranty.

 

I hear you wjtracy. If I were the type of person that likes to squeeze the last bit out of a car that would make sense. But I'm the type of person who doesn't like things to be broken. It would drive me crazy to know my battery has failed sufficiently to cause an 8 to 10 mpg drop. While we have an alternative vehicle this is our primary to take our son to school (two round trips a day total 52 miles per day), three or four 1,100 mile round trips a year, etc. I like to keep things in tip top shape. There are rarely things in my house that are in need of repair.

So if I determine the traction battery is going bad - out it will go. I don't consider $1,800 an unreasonable expense. By my calculations We've saved between $7,000 and $9,000 in gas compared to the other car we considered back in 2008 which was a regular gas Civic. Spending the $1,800 will give me peace of mind and we'll still be $5-$7K ahead on fuel cost. Besides we just like the car.

 

Sounds right to me. Even my wife is noticing it now. The mpg drop is obvious but now she sees the battery charge indicator rapidly dropping into purple multiple times a day.

 

If this is true then the Toyota dealer should have the same ability to check the battery. I have an appointment in the morning. If they find nothing I'll have to decide what to do. Perhaps the VCI cable and Techstream would make sense at that point. If they say the battery needs to be replaced I'll replace it. I have no interest in diagnosing the battery and replacing cells. It is possible Toyota will find something else wrong which would be less expensive to fix which would be great.

I am fairly convinced the traction battery is bad.
- We've been through 4 previous Redding CA summers with extreme high heat and the car didn't behave this way.
- I rather doubt the battery cooling fan is all that dirty because we rarely ride with the windows open, have no dog or other animal that would bring dirt into the car, and we keep the car very clean. No doubt there will be some dust in the fan but I doubt it would suddenly cause a shift from 45-48 mpg to 36-38 mpg from one tank to the next.
- The rapid drop from 7-8 bars to purple and back again several times a day is clearly a battery issue, or perhaps an ECU/charger. Hopefully Toyota can tell me that.
- Tire pressure is good.
- Brakes are not dragging.

My hope is Toyota will say the battery is bad. That would be a clean decision and the problem would go away with the installation of a new HV battery. If they don't find the battery bad my saga will continue.