1. Attachments are working again! Check out this thread for more details and to report any other bugs.

Question re: 12-volt battery, please?

Discussion in 'Gen 2 Prius Main Forum' started by Julia2001, Aug 14, 2012.

  1. Julia2001

    Julia2001 Member

    Joined:
    Aug 11, 2011
    290
    31
    0
    Location:
    Maine
    Vehicle:
    2007 Prius
    Model:
    II
    Good morning, friends.

    I tested my 12-volt battery using the following method as described elsewhere in this forum:

    DO-IT-YOURSELF TEST PROCEDURE (thanks to jdenenberg):
    - Without brake pedal, press the Power button once and release to enter ACC mode
    - Press and hold the MFD Info button, then turn the headlights on and off three times to enter Maintenance mode; release Info button
    - Press “Menu” (on screen)
    - Press “Display Check”
    - Press “Vehicle Signal Check” - the battery voltage is shown and should be about 12.4 to 12.8 Volts (normal for an unloaded battery)
    - Again without brake pedal, press Power button and release to put a current load on the battery - the voltage should stay above 12.0V (if less than 12.0V the battery is not well, or there is a fault or unusual load somewhere)
    - Press brake pedal and press Power button once to enter "Ready" mode - the battery is now charging at about 14V (if less than 13.6V or more than 14.4 there may be a problem with the charging circuit)
    - Turn car OFF to leave Maintenance mode


    My battery voltage shown under the "Vehicle Signal Check" is less than 12.0. It seemed to stay right around 11.7.

    However, when I go to Ready mode the battery is charging at 14V.

    So...it seems the first check is violated but the second is on target.

    My question, of course, is does my battery need to be replaced? I am having no issues currently. It's a 2007. I purchased the car used and do not know if the 12v battery has ever been changed.

    Thank you very much.

    Julia
     
    jdenenberg likes this.
  2. ksstathead

    ksstathead Active Member

    Joined:
    May 1, 2007
    1,244
    243
    0
    Location:
    Kansas
    Vehicle:
    2010 Prius
    Model:
    III
    I'm just an accountant, so take my free advice with a large grain of salt:

    Get a digital multimeter ($10-20?) and test the voltage at the battery posts to confirm the 11.7. My 2010 tells me a similar result, but the measurement at the battery is fine. If anything, I think I have a poor ground somewhere.

    Consider getting a BatteryMinder Plus (~25 iirc) or similar to charge and then desulphate the battery when it will sit for a while. Doing this on occasion seems to help mine. This advice is most appropriate for those with many short trips.

    At up to 5-6 years of age, your battery is likely not far from end of life. Winter usually kills weak batteries when cranking the engine is harder, but Prius 12V does not crank the engine, so more likely to have an issue from the heat, but it could go at any time. Being far from AZ heat, your battery should last longer than average.
     
  3. edthefox5

    edthefox5 Senior Member

    Joined:
    Jul 25, 2007
    10,096
    4,795
    0
    Location:
    Clearwater, Florida
    Vehicle:
    2007 Prius
    Model:
    Two
    Yes it needs to be replaced.
     
  4. uart

    uart Senior Member

    Joined:
    Sep 7, 2009
    4,215
    1,200
    0
    Location:
    Australia
    Vehicle:
    2005 Prius
    Unfortunately the 14V doesn't really tell you very much about the battery, only that the DC-DC converter is working correctly to charge the battery.

    The 11.7 reading says that your battery is not particularly strong and probably needs replacing soon. But can you be a bit more specific. After leaving the car off for several hours, and with all other accessories (A/C fan defrost radio etc) off, what is the voltage

    1. When you first enter the "signal check menu" from accessory mode, and
    2. After you hit power-on a second time (without foot on break) to place it into Ig-on (but not ready) mode.
     
  5. Julia2001

    Julia2001 Member

    Joined:
    Aug 11, 2011
    290
    31
    0
    Location:
    Maine
    Vehicle:
    2007 Prius
    Model:
    II
    Thank you, uart. I will try this tomorrow when the car has not been driven for a while, and I will report back with the result.

    Thank you again.

    Julia
     
  6. Julia2001

    Julia2001 Member

    Joined:
    Aug 11, 2011
    290
    31
    0
    Location:
    Maine
    Vehicle:
    2007 Prius
    Model:
    II
    Thank you very much for these thoughts.

    It actually has been VERY hot here lately...could be the culprit, I suppose.

    I will try uart's suggestion tomorrow and report the results and go from there.

    Thanks so much for your response.

    Julia
     
  7. jdenenberg

    jdenenberg EE Professor

    Joined:
    Nov 21, 2005
    3,831
    1,824
    1
    Location:
    Trumbull, CT
    Vehicle:
    2020 Prius
    Model:
    LE AWD-e
    Julia,

    11.7 volts is too low. Either your battery is due for replacement, or it has not been fully charged in your use of your Prius. Short trips (10-20 minutes or less) will not get much of a charge into the 12v battery. Long trips give enough time for the slow "constant voltage" charging system in our Prii to get the battery charged. If your use is mostly short trips, then the earlier suggestion to use a "Battery Minder" (it safely charges a battery at a low rate and automatically will not over charge it) overnight to top off the charge.

    JeffD
    ps: thanks for reminding people where the quick testing procedure came from.
     
    cwerdna likes this.
  8. Julia2001

    Julia2001 Member

    Joined:
    Aug 11, 2011
    290
    31
    0
    Location:
    Maine
    Vehicle:
    2007 Prius
    Model:
    II
    Thank you very much. I take very short (around town) sorts of "trips", and also longer, 20-30 minute trips for the most part. Once a month or so, 75-80 miles (one way) or so.

    It is astonishing to me that we have a car that requires lengthy trips to survive! But it does sound like I need to look into the "Battery Minder" you and ksstathead have kindly mentioned.

    Thank you so much.

    Julia
     
  9. Julia2001

    Julia2001 Member

    Joined:
    Aug 11, 2011
    290
    31
    0
    Location:
    Maine
    Vehicle:
    2007 Prius
    Model:
    II
    Hello again, friends.

    I am concerned about this need for a Battery Minder to be plugged into my 12V battery on a regular basis. Just another thing I DON'T need to deal with. Furthermore, I've been running the car (same short trips on a daily basis) for one year now, and I have never had a batter issue. HOWEVER....a.) I do not WANT to have a battery issue, and b.) I suspect my gas mileage might be better if I use the Battery Minder.

    My question: Would either of the following be reasonable for a 2007 Prius?

    Battery Tender 800 Waterproof 12V Battery Charger : Amazon.com : Automotive

    Or...

    BatteryMINDer Model 12117: 12 Volt 1.33 Amp (12V 1.33A) Charger/Maintainer/Desulfator : Amazon.com : Automotive


    And finally, all this talk about the battery, and all of my research hours on this board have me somewhat paranoid about needing a jump some day and having to rely on a AAA person or a good Samaritan which sounds potentially dangerous (to the car), so would this be something I should buy and store away in the back of my car (remembering to charge it now and again) for that purpose?

    Amazon.com: Jump-N-Carry JNC300XL 900 Peak Amp Ultraportable 12-Volt Jump Starter with Light: Automotive

    Thank you very much.

    I am going out to check the voltage on my battery while the car has been sitting cold all night and will report back. Still need the answers to the above questions regardless of the result, though, so wanted to post those for now.

    Thanks so much again for all of your guidance.

    Julia
     
  10. Julia2001

    Julia2001 Member

    Joined:
    Aug 11, 2011
    290
    31
    0
    Location:
    Maine
    Vehicle:
    2007 Prius
    Model:
    II
    To uart...

    In response to your questions:

    1. In ACC mode it reads 12.0. Then I heard a fan go on for a second and it read 11.7 for that second, but when the fan shut off it read 12.1 and remained there.

    2. In Ig mode it initially read 11.6 for less than a second and went to 11.8 and remained there.

    Diagnosis / prognosis???

    Thank you very much again for your time and guidance. I appreciate it all very much.

    Julia
     
  11. HaroldW

    HaroldW Active Member

    Joined:
    Mar 17, 2012
    716
    95
    0
    Location:
    Grand Forks BC Canada
    Vehicle:
    2014 Prius
    Model:
    Three
    Your battery appears to be showing signs of old age! I would replace it when budget allows. If you have manage to get around for one year without needing a jump, then I believe you drive enough to keep your battery charged. If you don't wont to bother with a 2 amp. tender then when you get home park your car and leave it in the ready mode [with E-brake on] for about 4 hrs.. Do this after replacing the 12v as the old 12v may not fully charge at this stage.. That should make your 12v happy! Just don't forget to go out and turn it off. H
     
  12. JimboPalmer

    JimboPalmer Tsar of all the Rushers

    Joined:
    Apr 14, 2009
    12,470
    6,862
    2
    Location:
    Greenwood MS USA
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    I own auto-polarity jumper cables, you CANNOT hook them up wrong.
    Michelin Smart Jumper Cables Surge Protection 5100 | eBay

    My 2009 has never needed a jump start, but I read horror stories here and decide I don't need to wait.
    My advice is to replace your 12 volt battery now, you know it can't actually store 12 volts. The car will waste energy trying to fully charge it and it can't hold a charge.

    The traditional replacement battery is an Optima Yellowtop, this site does great 'handholding'
    Optima DS46B24R Optima battery direct fit replacement for Prius 2004 +
    This year I have heard of an Exide battery that also fits. (more likely to be carried locally)
    Toyota Prius Starting Battery - Exide Edge 51JIS Flat Plate AGM
     
  13. Julia2001

    Julia2001 Member

    Joined:
    Aug 11, 2011
    290
    31
    0
    Location:
    Maine
    Vehicle:
    2007 Prius
    Model:
    II
    Harold and Jimbo...thank you both very much.

    How often do I need to allow a new 12v battery to remain on in the "Ready" mode for four hours to keep my new battery healthy?

    Thank you again.

    Julia
     
  14. uart

    uart Senior Member

    Joined:
    Sep 7, 2009
    4,215
    1,200
    0
    Location:
    Australia
    Vehicle:
    2005 Prius
    Hi Julia. My 12V is still original so it's not that sprightly either. I've probably got a bit of an advantage in that it gets driven about 2 hour most days.

    I'm currently getting 12.1 volts at acc mode (with all accessories turned off) and about 11.8 once I power it into ig-on mode. So as you can see, pretty similar to yours. I'm keeping a very close eye on mine as I know it will probably need replacing soon (its 7 years old already!). Maybe I've just been lucky, but I've not yet had any occasions where jump start was required.

    I'm not sure what the fan was that you heard running? It's best to have all the accessories turned off (inc radio, fans demister, lights, door lights etc) when you do that test. The idea is to get one measurement of the battery voltage while it's supplying as little current as possible (the acc mode measurement) and then a second one at Ig-on mode where the battery load is about 10 amps (to power all the ECUs and systems).

    Ideally you'd like to see about 12.3 volts or more for the acc mode measurement and about 12.0 or more at Ig-on. Those aren't "fix" values if you know what I mean. Based on my own measurements and what others here have reported that just seems to be what's typical for a battery in ok condition. A brand new battery would usually measure higher.
     
  15. ksstathead

    ksstathead Active Member

    Joined:
    May 1, 2007
    1,244
    243
    0
    Location:
    Kansas
    Vehicle:
    2010 Prius
    Model:
    III
    How many miles do you drive per year? If it's over 10,000 miles and kind of evenly spaced, you should be fine. Think about how many hours per week the car is in ready mode. That's how much time the 12V is charging.

    I suspect you don't need to do any of these things (BatteryMinder or Park&Run).

    ** Don't do the Park&Run in a closed garage (CO).**

    What sort of mileage are you getting? In the 40's? That's pretty good driving normally. Have you learned to glide with your foot slightly on the pedal (no arrows)? Techniques generally help more than a perfect battery. Only a truly failing battery really drags it down. (engine won't shut off, mpg drops inexplicably, etc).
     
  16. Julia2001

    Julia2001 Member

    Joined:
    Aug 11, 2011
    290
    31
    0
    Location:
    Maine
    Vehicle:
    2007 Prius
    Model:
    II
    Thanks a million, uart. Very important information for me, and I very much appreciate the time you took to explain all of this. Very kind of you.

    Do you carry any sort of jumper unit with you in your Prius? Do you use one of kthese "Battery Minders" or would you consider it? It seems that if our batteries have lasted this long, it shouldn't really be necessary, right?

    Thank you again for your very thorough response and for helping me to assess the health of my current battery. I'm looking now at the yellow Optima battery. It's pretty! ;-)

    Julia
     
  17. uart

    uart Senior Member

    Joined:
    Sep 7, 2009
    4,215
    1,200
    0
    Location:
    Australia
    Vehicle:
    2005 Prius
    If you're doing a few of those 20 to 30 minutes trips per week it should be enough to keep the battery kind of charged. A lot of people who don't drive very much probably do have their batteries perpetually undercharged to some extent (like in the 50% to 75% region). This is not really ideal, but since the Prius doesn't need a huge amount of 12V power to start it then you kind of get away with it. We really see a lot of people here getting lowish measurement (in that 11.7 to 12.1 volt range), which is definitely sub optimal, yet they do keep running. If you don't do anything to flatten it then it might still keep kicking for some time. On the other hand if you even just leave a front door open for a few hours (door light comes on automatically) then you might need a jump.
     
  18. Julia2001

    Julia2001 Member

    Joined:
    Aug 11, 2011
    290
    31
    0
    Location:
    Maine
    Vehicle:
    2007 Prius
    Model:
    II
    Ksstathead....thank you so much for your thoughts. No, I don't drive that much in a year. Probably more like 6,000 miles max.

    I do get in the 40's for mpg generally. When I first bought the car a year ago, it was quite a bit better, but that seemed to drop after my first tank or to of gas.

    I have been reading only recently about pulse and glide and am trying to condition myself to drive that way. Takes practice. But I do want to learn. Why not maximize the benefits of owning a Prius, I figure.

    Thank you again!

    Julia
     
  19. ksstathead

    ksstathead Active Member

    Joined:
    May 1, 2007
    1,244
    243
    0
    Location:
    Kansas
    Vehicle:
    2010 Prius
    Model:
    III
    Batteries usually are marked on top with the year and month sold; you could check that for its age.

    If the ICE shuts down at idle and in warm engine gliding under 41 mph, my guess is the battery, while likely weak, is not yet critically so. Work on techniques, and when the battery is later replaced, you'll know by whether mpg's jump up.
     
  20. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,198
    6,461
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    I agree that you should replace your 12V battery now.

    6,000 miles of annual driving is not sufficient to keep the battery charged. If you don't want to deal with hooking up a battery minder all of the time, an alternative approach would be to buy a battery charger and charge the 12V battery overnight, once or twice per month. The maximum charging current should be limited to 4A.

    Yes, you could purchase a jumpstart device but you will also need to plug that device into your AC house power outlet periodically to keep it charged.