How to Maintain 12V Battery?

Discussion in 'Prius c Care, Maintenance and Troubleshooting' started by visionseeming, Jun 27, 2020.

  1. visionseeming

    visionseeming New Member

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    Hello Everyone,

    As I mentioned in my introduction, I've been the proud owner of a 2013 Prius C Three since the end of July 2019. At that time, I drove the car to/from work everyday, and some weekends would make longer trips to visit family (~80 miles each way). So the State Of Charge (SOC) of the 12V Battery never crossed my mind.

    In fact, I never even disconnected the battery or checked its voltage after buying the car, worried about losing security system programming and re-programming my keys at the dealer for an expensive price. As far as I know, this is the original battery (will take pictures later and post to confirm).

    However, the pandemic has changed everything, and now I probably drive to/from work once every week or two, and manually maintaining the 12V Battery's SOC is essential. I visit family maybe once a month, and last weekend I went down, I didn't even take my Prius C.

    I am using a (750mA max) battery tender to charge/maintain the battery, but I'm a little unsure of the best way to set things up.

    The main question is "should I disconnect the black (negative chassis ground) terminal before I connect the charger, and why?" The Prius C owners' manual, clearly states in §4.3 (Do-it-yourself maintenance):

    upload_2020-6-27_12-34-25.png

    In contrast, the battery tender manual, states:

    upload_2020-6-27_12-43-37.png

    So Deltran wants you to leave the negative terminal connected to the battery, and connect the negative charger clip to the chassis away from the battery.

    After recent terrible experience getting another vehicle in our family (a 1998 Plymouth Grand Voyager) to pass emissions testing, I have learned that I should do everything in my power to avoid disconnecting the 12V battery in a modern vehicle for any significant length of time. We had to waste a lot of time/fuel trying to get all the I/M Readiness tests complete before we could have it tested, after I had let its 12V battery get too low and the ECM lost all its memory.

    Coming back to the Prius C, I think the best option is to leave the negative terminal connected, and connect the charger clips directly to the battery posts. I don't see any other obvious place under the rear seat where the battery is located, that I could connect the negative charger clip. Please let me know if anyone is aware of such.

    For full disclosure, last month, when I first charged the Prius C's 12V battery, I did in fact disconnect the negative terminal per OM. I lost a lot of saved information (e.g trip logs) and the date/time setting, etc. I now also fear I have lost all of the I/M readiness information, and I'd need to build that back up through regular driving. Luckily, I am not due for an emissions inspection until next year, but who knows how much I will be driving until then.

    Sorry for the wall of text, but I appreciate anyone taking the time to read, and offering any advice!
     
  2. アレン・スピクタロン

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    I think it is better to remove the battery for safety reasons, but don't charge it while it is connected to the car since i think it could damage something. About losing your trip data, date and time, well you could take pictures of those or something like that, since the 12V battery will eventually need to be replaced so you will still lose that data.
     
  3. sam spade 2

    sam spade 2 Senior Member

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    No, no, NO. Totally wrong.
    First, is this "battery tender" really a smart automatic charger ? Or a cheap trickle charger ??
    There is no need to disconnect anything to connect a good quality automatic battery maintainer.

    BUT.....despite your best efforts, that battery WILL wear out eventually.
    And 7 years is near the top end of it's expected life.......even if pampered.
    When things really start getting back to anything like normal, you might want to shop for a new one.
     
  4. visionseeming

    visionseeming New Member

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    Sorry, I had intended to link to the charger in my original post while editing, but forgot to :p.
    Here it is: Deltran Battery Tender Junior 021-0123. (I guess I don't have enough posts yet to provide the link, but you can find it on Google easily).

    Mine is a slightly older model than the one pictured, but the features are the same.

    Yeah, I'll keep that in mind. The previous owner was driving the car fairly heavily (long highway commute daily), so I believe the battery was kept charged by the Prius's inverter system automatically, with no manual intervention needed. For now I just want to keep it alive to avoid losing any critical information (like I/M readiness and smart key/security system programming). And in decent enough condition to be able to drive the car around when needed. :)
     
  5. Mendel Leisk

    Mendel Leisk Senior Member

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    I've always charged the battery while connected. The last few years I'd hazard the battery spends more time on a charger than not. In the Prius c Owner's Manual 3.5 amps is suggested as max charger rating. I would recommend something like CTEK 3300 (3.3 amp). Whatever you get, it should be a "smart" charger, capable off assessing the battery, doing a multi-stage charge and taper off to maintenance mode.
     
  6. sam spade 2

    sam spade 2 Senior Member

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    That tender is fine......for a tender. It will NOT reliably recover a DEAD battery though......and neither will the car by itself.

    You should NOT lose any "critical" information if the battery goes low.......or while changing it out.
    What is I/M readiness ??
    Radio presets and some personal preference settings might need to be reset but nothing associated with the actual operation of the vehicle.
     
  7. visionseeming

    visionseeming New Member

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    The I/M readiness monitors are the self-check routines for the various systems that control emissions (e.g. evap, O2 sensor, cat converter, etc.). They require certain specific driving conditions to complete, and if they are incomplete, you will fail the CA SMOG test, even if the engine is otherwise in perfect condition. We recently went through a lot of grief because of this very reason on another vehicle (1998 Plymouth Grand Voyager), which I had let the battery get too low (could no longer start the engine). I hope I haven't already lost this information when I disconnected the Prius's battery, but I don't have my Dad's OBD-II reader with me at the moment to confirm...
     
  8. sam spade 2

    sam spade 2 Senior Member

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    I think you will....or did.....because they are designed that way on purpose so you can't clear out stored codes without leaving some evidence.
    The technology has improved quite a bit since 1998 though.
    It has been discussed here a few times and the only complaint seems to be that sometimes you have to drive a little farther/longer that advertised to get it all back to normal. If you wait until your inspection is about to expire, that might mean that you are driving illegally for a few days.
     
  9. visionseeming

    visionseeming New Member

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    Thanks Sam... I know it sounds like I'm making a big deal out of it, but it is just a lesson learned for me given the recent experience. Anyway, I currently have the battery tender connected to the battery posts, with the ground cable connected to the battery. So far, no issues.

    I'm seeing an "idle load" voltage (i.e. battery tender disconnected overnight, power switch off, security system disarmed) of about 12.4V. I didn't want to disconnect the battery to measure the passive current draw. With the battery tender connected (and in maintenance mode i.e. solid green light) I see around 13.1V.

    I will not disconnect the negative terminal anymore, until I have to replace the battery.
     
  10. sam spade 2

    sam spade 2 Senior Member

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    Well 12.4 with absolutely no load is low......or getting low.
    BUT the way you measured it might NOT be "no load".

    If the battery really has been in service for 7 years, you might as well locate a replacement NOW.......because you likely will need one soon. I would be replacing it at MY convenience, not when it finally decides to fail at some random time.
     
    Mendel Leisk likes this.
  11. Mendel Leisk

    Mendel Leisk Senior Member

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    7 years old? Yeah, why are we talking lol.
     
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