Time to change the 12v Battery?

That mileage seems about right for winter driving, summer should get you 5+ mpg more.

We have an '08 w/ 145,000 miles 42-49 mpg.,depending on the temp, and length of drive. We still have the original battery.

How many miles on the car?
What part of the world are you from?,
Outside air temp and miles per trip can make a big difference in mpgs.

10% for cold, 10% wintergas, 10% short trips.
Assuming
50 mpg summer
Ballpark results
45 mpg winter gas 20+ mile trips
40 mpg cold 10-20 miles
35 mpg short trips in winter, < 10 miles

Changed the trans fluid at 40K, and was getting 43-50 mpg. About 2 years ago with 130,000 miles, the mileage dropped to 35-40 mpg, I changed the trans fluid and the mileage went back up.

 

The Toyota Dealer will have a battery with a 84 month warranty, as long as anyone.
If you prefer third party.
amazon.com/Optima-Batteries-8171-767-DS46B24R-YellowTop/dp/B006VFEJJQ

 

This really helped answer my MPG questions with my 2005 Prius. I've only owned mine for about 5 weeks and I was averaging about 38-39 MPG. It has been colder in Seattle in the last 5 weeks, I believe winter gas is still in effect, and have been driving less than 20 miles each trip. When we did take it on a road trip down to Portland, OR, we averaged about 43 mpg. All of this was before I took my Prius in for service:

1. Oil change
2. New engine air filter
3. New cabin air filter
4. Transaxle fliud drain & refill
5. Throttle body cleaning
6. New rear brakes
7. Brake flush

I haven't driven it far since filling up after the things were done. The weather is starting to warm up and summer gas should be here soon. I hope to see increase of MPG soon. I am also getting better at hypermilling.

 

Can you check it with the car off with a digital volt meter?

Sounds like it does need changing, but get a clear measurement first.

 

I bought my 2005 Prius about 5 weeks ago and the previous owner does not remember if he replaced the 12v battery or not. I ended up getting it replaced to be safe. I bought a Toyota TrueStart battery from a local dealership. Like @JimboPalmer said, it comes with a 84 month prorated warranty. Another member here told me that the Duracell one from Batteries Plus is pretty good too. That one comes with 48 month warranty. Currently there is a coupon code to save 10% off if you buy online and pick up in store.
SLI51PAGM - Duracell Ultra Platinum AGM Battery for 2007 Toyota Prius L4 1.5L Smart Key 325CCA Car and Truck at Batteries Plus Bulbs

 

Those voltages seem a bit low (except Ready, which is not relevant here). But I'm not so sure it is low enough to have noticeable MPG impact. Some folks who have replaced the 12V battery have not seen an improvement.

There could be other issues to address too. This questionnaire will help identify most of them:
Fuel economy complaints/queries? Please copy, paste &amp; answer these questions, esp. if you&#039;re new | PriusChat

 

welcome!
how many miles on her?

 

crap or under inflated tires will drop your mpg too. inflate to 40psi and see what you get.

 

agree with most of the above. it may be getting time for a new 12v, but you might need some other work. tires? pressure? throttle body/ mac? and etc., have you done all the regular maintenance?

 

The battery is probably due to be changed, but not an emergency. Start shopping around. You got some good tips above. I also found the Toyota dealer to be competitive last time I bought one.

At best, a new battery might improve your mileage by less than 5%, I hear.

 

The only way a 12 V battery will have any noticeable impact on MPG, is if it is in such a state (shorted cell, severe sulphating, etc) that it is constantly drawing a high current, without actually holding a charge.

I don't believe your battery fits this bill, it just sounds neglected. Charge up that battery and move on to finding the real problem.

 

One thing i have noticed is an increase in mileage by replacing the Inverter coolant. The Inverter coolant has a rough life. Efficiency is keeping the Inverter happy its the heart and soul of the car. I have replaced mine twice now at 110K.

If you have recently purchased the car and not sure of the battery's age at the numbers your seeing replace that battery at your leisure asap.
I say that only because of the thousands of posts on this site about people who damage there car getting stuck with a dead battery and doing the battery jump incorrectly.

Posts about the 12 volt battery in this car are the most frequent post on this site. A poor 12 volt sneaks up on people because there's no sound of a low battery you may hear as you attempt to start the car as a warning as starter turns slowly. There's no starter in this car. One day a very marginal battery will just show you a dashboard of lights and nothing else. Usually in a bad time. Forcing a jump start. Then the horror begins.