10 mpg loss --->SOLVED!

I agree with uart, that seems low. I've worked through Alaskan (Aleutian) summers when it snowed on me, but never winter. However, when my Tundra was parked outside in Georgia I had battery trouble when temps dropped into the teens. I had (have) a voltage indicator in the 12V accessory jack and read it in the low 11's without any appreciable load and it had trouble cranking. I had to exchange the battery (Wal Mart batteries aren't much good, but they are essentially free after the first one...think I'm on #3 for the truck now and may never pay for a new one again at this rate.)

But I'm hesitant to blame this on the aux 12V battery alone. At 0-10F it takes forever to warm the Prius up, even with grill blocking. It really is not just the engine. There are protocols for battery temperature which also impact engine and HV battery operation. The hybrid battery is still cold and its output is minimal at this temperature. So the engine runs more to heat the battery (forced charging) and because the battery can't supply the amps when required for traction/accessories (as in the ~800W electric heater.)

I claim no credit for learning this. One of our Japanese PC members provided most useful charts for the hybrid battery output with temperature. It was an epiphany for me when he explained it.

It's a gamble as to whether the dealership is right or not in your case. My suggestion is to ask to comparison drive a new one, read its voltage and run a 10 mile circuit to see what the mileage does. I don't know whether the dealership gets reimbursed by Toyota for batteries in new cars. When the dealership knows Toyota is paying (e.g. a recall or TSB they can be very helpful. But when it is coming out of their pocket...not so much.

 

This must be my problem. My dealer has been no help, but the MPG drop seems permanent. All I have to do is look at the display...transitions no longer make any sense. If the Prius is supposed to be on battery only at 5 MPH, it just switches back and forth.

 

I'm hesitant to believe the dealer, but at this point I either shell out the $$ for a new battery and *hope* that makes a difference or just wait for it to warm up.

 

At 92K miles I changed the original equipment 12V battery on my 2004 as a preventive measure, three weeks ago. The old battery measured 12.2V in the morning with the car IG-OFF, after being parked overnight with low temps in the high 30s F. The new Toyota battery measured 12.9V out of the box. (all measurements per my Fluke 87 DMM.)

I did not think that it was reasonable to expect an mpg increase after installing the new battery. However after driving three weeks with the new battery, mpg per MFD is in the high 40's, while it previously was in the low 40's. So I would say ~5 mpg improvement from the new battery, as reported by the MFD.

 

I didn't wait until our OEM battery was mortally wounded ... in stead opting to go optima at 75K ish miles just as a precautionary PM. So, I never noticed a drop in mpg's. Heck ... this ol' dog learned a new trick!

.

 

Very interesting!
I've owned our 2007 Prius for about 6 months. It always seems to be getting an avg mpg of 43.5 mpg, no matter what I do. I lowered the oil level to the "1/4 inch below fill line". I have the tires at 41/40psi.

I drive like an old lady...(except for our recent trip to Florida....85mpg on I-95). Still averaged 43.5 mpg. Highway, city, long trips, short trips, around 43 mpg......cannot get it to go higher.

I asked my dealer about it, he said, "That's the best you can get around here....it's the 10% ethinol..........if Priuschat folks are boasting more they are lying". That's What he said. ( I DON"T believe that....you guys are GREAT!)

Next I plan on trying Synthetic oil.....I was going to try buying Premium gas without ethanol down in Florida, but did not know if it was worth it or if the higher octane would hurt things, so I did not.

On a regular check-up, my dealer told me my car "threw a code" saying a low battery...but they told me it was "ok", but asked if I did anything to drain the battery some. I told them I did nothing. I then took it back about a month later, just before the trip to recheck the battery, and they did not tell me any numbers, but told me the battery was "fine".

It currently has about 57,000 miles on the car. Now that I read this, I am wondering if the battery is hurting my mpg....??

My question is, since I am starting not to trust the dealer, can my other mechanic who works on my other non hybrid cars check the battery for me? Is it just getting to it and clipping a meter on it? Does he need a fancy machine that hooks somewhere under the dashboard? Could he hurt anything? Do I need to return to the dealer?

What numbers should I be seeing, etc? I'm beginning to think I should just upgrade to the better battery and never have to worry about it again, since it is 3 years old and I am not sure how long it SHOULD last.

Thank you in advance for your kind help. I love my Prius, but am a bit intimidated by it.........

Frank D.

Thank you in

 

FrankD did they tell what code it was???? Checking the 12volt battery is no problem it's just like checking a normal battery.

 

Thank you. They did not tell me the code.

In light of this thread, I think I need to do a bit more checking.

Frank

 

I installed the Optima battery. I have not driven enough to check mileage, but my radio works again. My radio kept losing the station as the old battery aged.

 

My wife's Prius was getting around 43 MPG and hardly more .We bought wrecked Prius from US and imported it in EU. I don’t know exactly how long car was not powered in wreck yard or was battery charged before car was loaded into ship for transportation Anyway when we got the car the 12v battery was not dead and was able to power up the system. So after car repair I didn't bother myself with 12 battery charge. After investigation how much MPG other Prius owners gets I come to conclusion that something not right with car J When I have read this post I decided to give a try and charge 12v battery before buying new one. The result is that after one week of driving, my wife is getting 47 MPG when temperature is about 45-50 F.

 

See this thread for checking the battery yourself:

http://priuschat.com/forums/gen-ii-...has-cold-weather-done-my-beautiful-prius.html

 

Dear Richard,
I just did the check on my 2007 Prius, doing it the way outlined in the other thread, (pressing the power button, etc).

The reading I got was 11.9, 11.8 when you said it should be between 12.4 and 12.8.

The second check, (when under load) was 11.7

The third check, (pressing the power button while pressing the brake pedal) was 14.1

So, the first and second check numbers were according to the post, not good. The 3rd check being 14.1 was within normal limits. If I am understanding this correctly, this is telling me that my battery IS charging ok, but that it is weak, and on it's way out. I did this check in my garage, where the temp is about 40 degrees.

Just after I bought the car, I had an issue with the radio volume not working with the knob, but working with the steering wheel control. This was intermittent. When I brought it in to have it checked, the mechanic told me that the Prius had a "code" in it saying "low battery", and asked me if I messed with it at all adding any aftermarket stuff or anything. I told him "No way". He said the battery seemed ok, and he cleared the code and sent me off.

This worried me, so I went back Sept 1st and had them recheck the battery, before I took the trip to Florida. They told me it was fine.

Now, I've been getting poor gas mileage....(43mpg). Now I learn there may be a correlation. Now I learn how to check the battery itself. Now I learn that it IS bad.

I think I'll be seeing the dealer tomorrow. My warranty is now expired, but I think this should be covered because of the evidence if an existing problem during the warranty period. If they do not think so, it is still covered under the certified warranty, where I pay the first $50.00, I believe. The question is, do I pay that much for the Toyota stock battery, or do I say the heck with them, and pay the $160 for that better Optima retrofit battery........

What do you think? Thank you all in advance for your kind help.

Respectfully, Frank D.

 

[frickin' frickin' frickin slow servers!]

 

Yes, the charging system is fine, and the battery is dying. I'd also look for a new dealer, one who can test batteries properly :_> The old one should honor the warranty. Getting a new Toyota battery even with dealer installation is not a bad choice.

Read through the eLearnaid Optima installation instructions before buying. You will need all of the tools listed, and, unless you also have a bench vise, a lot of hand strength to dis-assemble the original positive terminal assembly.

 

Thank you Richard!

I'll go see the dealer tomorrow to see what they will do for me. Sadly, the next closest dealer is 35 miles away.....but I agree I do not have that much faith in this local one.

If they refuse to do anything after we tangle, then my plan B will be to order the Optima battery. I try not to do too much car work during the winter, but I do have a mechanic friend who will let me use his heated garage bay, tools, etc. If I have to I'll have him help me with it. I also agree that I'd rather have a new free (or $50.00) Toyota battery then have to pay $160 for the better Optima battery.

The question is though.....is the optima battery so much better that the better choice be to just get that? Would the optima battery be "overcharged", and perhaps give better gas mileage then a new Toyota battery?

I guess the question is moot.....I need to see the dealer tomorrow.

Thanks! Frank D.

 

Hard to say. It should last longer, but I can't predict how much.

It will not be "overcharged". It is possible that the car has been wasting a noticeable amount of power trying to keep the old battery charged, in which case you may notice increased MPGs.

In any case, enjoy!

 

Well, I went to my dealer this morning. Just before I left, I did another system check. This time the numbers were a bit higher- 12.1 and 12.0 under load. This was after sitting in the garage all night. I did do about 75 miles of driving yesterday.

The time before, when I got the lower numbers of 11.9 and 11.8 was after the car sat undriven for 5 days.

So, the dealer checked it using his fancy toughbook looking laptop, plugged into a outlet under the dash. He said it was not showing any codes, and that his unit said that the battery was good. I asked him what numbers it was showing, and he replied that it does not show numbers, just "good" or not. He then went on to explain that his machine was very good, and detected bad batteries even before they were close to being bad, and that mine was perfectly fine. He then asked how I got my numbers. I showed him how I got into the menu, etc, and showed him the numbers.

He was surprised, telling me "No one knows how to do that"! And that those numbers do not really mean anything, because they can vary dependent on if your radio or heater fan was on prior, etc, etc. Bottom line...the battery is fine in their opinion and not in need of replacement. So the dealer doing something "under warranty" is not going to happen.

So.....not to beat a dead horse, I have to decide what to do. The numbers were up higher this morning, and nothing has gone wrong...yet. The mechanic told me not to do anything until the car fails to start, or does "funky things"....that it probably has a long time left on that good battery before anything happens.

So, if the numbers are supposed to be at least 12.4, and at best, it is at 12.0.......does that justify replacement? I'm leaning to think that it might, but you guys are the experts. Giving weight to the replacement decision is the possibility of increased mileage. I do not want to wait for bad things to happen to replace it. Then again, if I have another year or two before it gets "bad" according to the mechanic...perhaps it is to early too think about replacement.

I'm leaning towards replacement.....

You guys are great. I appreciate your input! Thank you!

Frank D.

 

The dealer is correct that voltage varies under load, but the instructions given here produce a fairly constant load.

It sounds to me like your battery is still serviceable, but getting into its golden years. If you are a cautious person you can replace it out of pocket, otherwise wait a bit and see if it gets bad enough to have it replaced under warranty.

Tom

 

Ditto Tom.

The "good" idiot light threshold on that dealer's tester might be as little as 10V. That's OK for old-technology cars, but Prius (like many modern cars) is demonstrably sensitive to low voltages. But if that's what that dealer knows then you're stuck with waiting for it to deteriorate further, replacing it yourself now, or trying a better-equipped dealer.

 

It sounds like a function on the TechStream laptop - probably the simple 'Health Check' display or something. The Data List view would show the actual voltage.

Also, if they put the car into READY rather than just ACC (green light on the power button), it would have seen the DC/DC converter's output voltage, not the battery voltage.

TechStream is Toyota's official scan tool for communicating with the car's ECUs. It's not cheap at $8,000. They've just started to offer 'TechStream Lite' where you supply your own laptop and they provide a USB interface to the CAN bus and the software to drive it. It's still $1,345. Compared to TechStream you only get one year's TIS subscription rather than two, and it only supports the DLC 3 connector (1996 model year cars and newer, rather than right back to 1989).