What causes a 12 volt battery to be always drained? It will be drained if sitting over 1 hr

Discussion in 'Generation 1 Prius Discussion' started by JaneWalt, Jun 12, 2021.

  1. JaneWalt

    JaneWalt New Member

    Joined:
    Jun 12, 2021
    1
    0
    0
    Location:
    CT
    Vehicle:
    2002 Prius
    Model:
    N/A
    I am looking for help in diagnosing the problem with my 2002 Prius. I am wondering if something other than the hybrid battery or battery cells could be to blame for my 12 volt battery being drained if not driven constantly. It started out that the car would start if driven daily, but now the car cannot be left even for an hour without something drawing charge from the 12 volt battery. The 12 volt battery itself is perfectly fine. Could this potentially be an issue with the inverter?
     
  2. Sandy Meyers

    Sandy Meyers Member

    Joined:
    Dec 17, 2016
    153
    56
    0
    Location:
    Los Angeles
    Vehicle:
    2002 Prius
    Model:
    I
    I feel your pain. However my car can no longer go more than 10 days without drawing down a brand new auxiliary battery. I don’t drive the car much and I do not actually set the alarm but rather the red light does remain on when I hand lock the vehicle with the key. I can’t figure it out and would surely like to know.

    You could have a bad 12 volt battery altogether. There must be some electronics in the car that simply drain on the car while parked. I can’t imagine the inverter is your issue since you’re not actually driving the car. Let’s see what the folks here have to say.

    I would be interested in knowing what electronic is likely draining the battery and if that device could somehow be disabled by pulling a fuse or if it is the alarm if a kill switch could somehow be installed for those who don’t drive the cars much.

    I have a trickle charge on hand but access to using that is limited and not a very functional device with the Gen 1 Prius. It cannot charge off the cigarette lighter and appears to have to charge off the 12 volt battery.
     
  3. Samuel Williams Jr

    Joined:
    Jun 4, 2019
    246
    87
    0
    Location:
    Dayton NV
    Vehicle:
    2005 Prius
    Model:
    Four
    Hmm I am not sure what your are doing here? A trickle charger ie Battery Maintaining need's to plumed into to an AC source to work?

    AFAIK the 12 volt sources on a Prius don't function if the car is off?
     
  4. Samuel Williams Jr

    Joined:
    Jun 4, 2019
    246
    87
    0
    Location:
    Dayton NV
    Vehicle:
    2005 Prius
    Model:
    Four
    Don't overlook the obvious first. make sure the interior lights the cabin or the trunk are not being left on? And yeah the headlights.

    One hour is pretty quick to drain a 12 volt battery? But back to basics, have you had the 12 volt battery load tested? Just about any Auto Parts store can do that for you. You need to start with that. :)
     
  5. ronlewis

    ronlewis Member

    Joined:
    Dec 5, 2016
    397
    99
    0
    Location:
    texas
    Vehicle:
    2001 Prius
    Model:
    One
    If you can get to a quiet place, you might listen for any motors running after shutoff. An hour is real fast for a battery to run down without something mechanical pulling it down. You could always pull a fuse or rig up a way to easily disconnect the battery. For example, I use the cheapo $22 riding lawn motor batteries from Walmart in my car. They don't last long but you can buy a bunch of them for the cost of a yellow-top. I keep a regular car battery in my trunk with jumper cables attached to the lawn mower battery. At this point, the lawn mower battery is no good. If I disconnect the jumper cables, it won't start. That's pretty easy to do - pop the trunk and connect one jumper cable.
     
    Samuel Williams Jr likes this.
  6. GabrielD

    GabrielD Member

    Joined:
    Oct 18, 2019
    174
    67
    0
    Location:
    Romania
    Vehicle:
    2014 Prius+ MPV
    Model:
    V
    Jumper cable must be attached in front, no need to open trunk...
     

    Attached Files:

    edthefox5 likes this.
  7. ronlewis

    ronlewis Member

    Joined:
    Dec 5, 2016
    397
    99
    0
    Location:
    texas
    Vehicle:
    2001 Prius
    Model:
    One
    I'll bow to the greater knowledge of others regarding how to jump start. Just saying, my way has worked for over a year now. There's no room under the front hood for another battery, so having to lug one up there to jump every time I start the car would be no good. But popping the trunk and attaching the black jumper to one battery is pretty easy.
     
    Sandy Meyers and Mendel Leisk like this.
  8. sam spade 2

    sam spade 2 Senior Member

    Joined:
    Mar 31, 2018
    5,745
    2,283
    0
    Location:
    USA
    Vehicle:
    2017 Prius c
    Model:
    Four
    What exactly makes you think that the battery itself is "perfectly fine" ?
    ONE incident of accidentally draining it down will often cause it to STAY low and that tends to make it fail completely in a fairly short time.
    The car takes a LONG time to fully recharge a drained battery.

    How old is the 12 V battery ?

    Testing the inverter is a simple matter if you have a voltmeter.
     
  9. Josey

    Josey Member

    Joined:
    Jun 10, 2019
    201
    84
    0
    Location:
    Virginia
    Vehicle:
    2003 Prius
    Model:
    One
    I just had to get a new 12V. I could get it charged up fully (by car or charger) and it would come out of it at about 13V (which is should have been), but within a short period of time - like a matter of minutes - it dove to 11V. It was only two years old (my replacement was free), and it wasn't the car doing it.

    As has been suggested, take it to a battery place and have it checked.
     
    Samuel Williams Jr likes this.
  10. Sandy Meyers

    Sandy Meyers Member

    Joined:
    Dec 17, 2016
    153
    56
    0
    Location:
    Los Angeles
    Vehicle:
    2002 Prius
    Model:
    I
    I may have misstated above.
    I’ll have to get back on this post. Something about the trickle charger and electronics meant that it would have to hook directly to the 12 volt and not charge through the cigarette lighter which is problematic in my situation. As far as the OP, I addressed it as well.
     
  11. Sandy Meyers

    Sandy Meyers Member

    Joined:
    Dec 17, 2016
    153
    56
    0
    Location:
    Los Angeles
    Vehicle:
    2002 Prius
    Model:
    I
    The 2002 Gen 1 does not have a place to jump from the front of the vehicle. You must jump from the rear of the vehicle. There are no posts as in later models. I know this and am a 2002 owner. I’ve jumped started the vehicle so many times. Be careful you do not reverse the polarity on the cables because it’s a PITA replacing the burned fuse and hopefully you don’t fry the inverter.
     
    GabrielD likes this.
  12. Josey

    Josey Member

    Joined:
    Jun 10, 2019
    201
    84
    0
    Location:
    Virginia
    Vehicle:
    2003 Prius
    Model:
    One
    There are solar trickle chargers.

    The 12V sources on all cars have to do stuff while the car is off. (e.g. the antitheft system). But it should be doing very little. However, various kinds of problems can end up creating too much 12V current draw - generally called a parasitic draw.

    My guess in this case is just a bad 12V battery.
     
    Sandy Meyers likes this.
Loading...