Weird stuff happening? MPGs dropping? Test The Battery

I have noticed a 12.0 and then a 12.35V reading on 2 occasions after the car sat for a couple hours or more.

Today, I got a 9.75V reading after the car sat in ON with the radio on for about 45 mins in my garage. I would think that even this small battery would do better than that. I did have the volume on low. After I started the engine it goes to 13.75V, then to 12.4 after the ignition has been turned OFF for 5 mins. I'm sure now after another hour is is lower yet.

Dying 12V battery?

 

This subject has been covered adequately, especially Richards comments. To really explore, read all post in search for 12V Bat or aux Battery. It is important to remember that the AUX only starts the computer which starts the car. So any 12V which fits or doesn't fit will make do in a emergency. Even two 6V lantern batterys in series. I always keep a spare in the car and have 2-3 in the garage. The spare is a block battery which I charge from time to time with the accesory plug in while driving on trip. Having adequate wiring also helps as a temporary emergency jump.

 

I've got a 2005 without the SKS. I drive it daily for work, and haven't had any issues with the car with two exceptions. Two years ago when I was on my honeymoon it sat at a friend's house and they couldn't start it. When I picked it up it was fine.

Today, I turned it on for moment to back it up in the driveway so I could clean leaves off the roof. When I got back in about an hour later, I noticed the keyfob didn't unlock the door (it was unlocked already, but I hit it out of habit). Then, I noticed the Check Engine light was coming on and fading out. The lights were turned off, as was the radio. The dome light things were very, very faded when I tried to turn it on to see to get my owner's manual. When I was sitting in the car while this was happening, I heard a sort of whirring sound from the car.

Am I probably correct in thinking this is a dead 12V battery? Can I get a new battery at the auto parts store, or do I have to go to the dealership? Will a jump start from AAA work to get me going? The nearest dealership is about 30 miles away from me.

Thanks!

 

I did turn the car off (keys were in my back pocket), so it wasn't that that killed the battery. I don't have the SmartKey system, so once the keys are out, it's off.

I've seen all the instructions about checking the battery - is it really relatively easy to get out? I'm relatively mechanically inclined, so I'm not afraid to do it myself, I just need to have decent instructions on it.

I'm hoping it starts tomorrow and I can just drive it up to the dealership.

Thanks for your input and help!

 

Joe,

I created that test sequence after finding out that "Maintenance Mode" was available in my 2004 Prius (Thanks to this discussion group) and published it in several of the discussion topics to help others decide on when to replace their 12v battery. (Mine is still good after 6 years and 171,500 miles )

Being an Electrical Engineering Professor has some benefits.

Christina,

Our little 12v batteries have about half the capacity of a normal car's 12v battery. Either can be weakened by a small number of full discharges or leaving one partially discharged for a while. You are probably due for a new battery.

Another issue is due to the method used to charge the 12v battery in our Prii. The battery is charged by putting approximately 14 volts (from an electronic supply generated from the big 200v battery) on the 12 volt lines. This safely and slowly charges the battery. So if you mostly make short trips, the battery never gets fully charged up and has a shorter life.

JeffD

 

Re: Weird stuff happening? Test The Battery: Here's How

If someone is as picky as I am that doesn't want to give the light bulbs unnecessary thermal shocks then he/she can use an alternative method to enter the maintenance mode. Details here:
http://priuschat.com/forums/gen-ii-...out-switching-headlights-off.html#post1095046

 

Re: Weird stuff happening? Test The Battery: Here's How

Thanks Richard, those are great tips.

Just had our 2005 in for routine maintenance, and the dealer says our auxiliary battery failed the battery test. The car has 85,000 km, ~50/50 mix hwy/city driving, max. summer temps are usually a few days of +30 C (86 F) here, and the last 6 winters have been warm for here; very few days below -30 C (-22 F). There were a few times where the Prius sat for 3-4 days at a time in the winter (when we had a lot of snow and I needed something taller with much better traction than our Prius gets on ice/deep snow).
Is it usual for the auxiliary batteries to die so quickly in Priuses? This is our first hybrid & first Toyota. We've never had any other battery give up the ghost before at least 100,000 km (60,000 miles), in 20+ years of driving.

(The only symptom of low battery has been slightly reduced mileage, but I chalked that up to the unusually windy days we've been having the last 3 or 4 years.)

 

Re: Weird stuff happening? Test The Battery: Here's How

5 ~ 6 years in your weather condition is pretty long for a Prius 12V battery. What does the maintenance mode read when the battery is under load (headlights ON for example)?

 

Hi Guys,

Great thread. MPGs can drop as a result of a dying 12v battery because ECU settings can get wiped (that is, ECUs like the one that controls the engine reset and lose their accumulated "learned" data about how your engine operates and what optimal settings to run it at based on fuel grade and such--relearning this data can take some time and by the time it does it has to do it all over again when the car restarts).

This data also gets cleared when you take your car in to have DTCs cleared which is why some people may see decreased mileage for the first drive after having the car serviced...

Andrew

 

Just replaced my 04 accessory battery at 55,000 miles (6 years old). It was discharging after sitting for a few days and the car wouldn't start. It did this three times in two weeks so I wised up and bought an Optima D-51 deep cycle battery locally. I used a bench grinder to alter standard battery cable ends to fit the old cables. Also, I used the grinder to lessen the diameter of the stock battery vent connector to fit in the smaller hole of the optima. I used gasket sealer to plug the vent hole on the other side of the optima. Works like a charm all for $144 from Advanced Auto parts. Bought online for a 15% discount on the battery (or any parts) and picked it up at the store.

 

Re: MPGs dropping? Clean the mass airflow sensor

Check out this thread:

http://priuschat.com/forums/gen-ii-...003-clean-mass-airflow-sensor-seems-help.html

 

This car amazes me with something new everyday. Thank you so much for sharing your wisdom and knowledge with the forum!

 

Re: Weird stuff happening? Test The Battery: Here's How

Finally got the readings on my 80K-old battery. Looks pretty marginal:

Unload: 12.2V
Load: 11.9V
Power on: 14.1V

Does this mean my battery has begun its final journey to the grave? (It died on my last week after being left alone for 5 days with SKS on).

 

Re: Weird stuff happening? Test The Battery: Here's How

It needs to be replaced. Draining our little 12v battery permanently degrades its performance. Mine is still going at 177k miles (6+years, still somewhat stronger than yours), but I keep a jumper battery in the back of my Prius "Just in Case" (the built-in air pump and light have come in handy).

JeffD

 

I've owned my 2004 prius for over 2 years and it's been great and mostly problem-free. Yesterday though, while driving on the 405, doing about 65, my cruise control suddenly cut off, and I got the dreaded "triangle of death" and the "turtle" on my MFD.

I continued driving and didn't notice anything unusual with the handling or performance of the car, and went about my day as usual, hoping I would not get stranded somewhere. I also drove many miles today and at one point, the warning lights disappeared, and I thought I was in the clear.

They soon returned, and so when I got home I started checking the internet for clues. I then starting thinking that the problem could be linked to my 12 volt battery; it came with the car when I bought it, and I don't know if the last owners ever changed it, or if they did, when that was.

So, I just tested the 12 volt battery using the maintenance mode check as outlined here, it was barely registering 12v while UNloaded, and then when loaded it dropped to 11.8. Then the final "charging" mode test was normal at 14.v.

So, would 11.8 under load be considered bad, and time to replace, and more importantly, could this be the reason for the triangle and turtle waring lights?

If so, and I go ahead and replace the 12v battery, will those warning lights automatically go off, or do they need to be reset, like when you do an oil change? Thanks in advance for any help.

PS: I've been reading about how a lot of people seem to rave about the Optima yellow top, with free shipping and so on. I really don't want to wait for it to be shipped to me, and can't seem to find one locally, so should I just bite the bullet and buy the OEM version from my toyota dealer? I'm somewhat mechanically inclined, but I'd rather have them or a qualified independent tech install it. And will the toyota 12v last a decent amount of time in SoCal conditions? I just want to get it done and over with so i can get on with things.