Hybrid battery, is too full bad?

Discussion in 'Gen 3 Prius Technical Discussion' started by Scaurex, Sep 12, 2010.

  1. Scaurex

    Scaurex Junior Member

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    We have 2 Prius, 2 different daily routes and drivers. BOTH cars USED to operate between the 3 to 6 bars of battery on normal daily commutes.
    About one month ago, we drove one car on a few hour trip with a lots of downhill on the way back home, I coasted/supplemented charging with the brakes and the battery was charged to 8/8 bars when we arrived home. It seemed to take a long time to finally get the top bar of the battery charged. Now in daily commutes (still one month later) the car operates between the 6 to 8 bars of the battery.
    My commute is about 50% uphill and 50% downhill of varying grades, I always ride the brakes to supplement the charging and bring my speed down as it's only a 60kph zone during my 13km/18 minute, all city traffic commute.
    I have deliberately run the battery down to 2 bars using EV mode, but after just one daily commute, the battery returns to 7/8 or full.
    Yes, i hear the battery pack cooling fan a fair bit if i drive the car more than 40 minutes, but not at all on the daily commute.

    We just did the same trip with our 2nd Prius, but it was on cruise control all the way home. The battery did not charge past 6 out of 8 bars.
    This car still operates in the 3 to 6 bar range on daily commutes.
    I've attached a couple pics of the display from each car. Car 1 did have 8 bars, but after being parked for 8 hours it has dropped to 7.
    Both cars have the same options, but the one with the full battery issue has 4400km and the other has 2600km.

    My questions are:
    1. is there such a thing as too much charging in the Hybrid battery?
    2. does having this full battery shorten, or increase the life of the battery?
    3. have i done any damage to the hybrid battery or is it bad for the car by having a full battery?
    4. It seems difficult to charge the 8th battery bar for the first time, but once it's been done once, it seems easy to achieve consistently. Why?
     

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  2. gbarry

    gbarry Junior Member

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    It's not possible unless there's a malfunction. And even then, one of the computers would probably show an error and disable the high voltage system.
    "A" (truly) full battery would have shortened life. But "this" full battery, no. You see, at 8 bars, your battery is only 80% charged, so there's never any chance of overcharging. Toyota built this "headroom" into the system to prolong battery life.
    I think you can see that you haven't. By the way, mine likes to run at 6 or 7 bars. But I don't have two cars to compare :)
    This one I'll leave to the experts. It is an interesting occurrance. I'd actually expect the opposite behavior if the computer decided that you do a lot of downhill braking.
     
  3. Colonel Ronson

    Colonel Ronson New Member

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    There are failsafes installed to prevent overcharging the battery. The battery meter is not representative of the full charging capacity of the battery.

    And it is easy to fill up the battery rolling down a hill, or doing a long coast after exiting on a highway ramp.

    Don't overthink it. Yes, you would have to worry about these problems in a inferior honda hybrid system, but not the superior Toyota Synergy Drive =)
     
  4. The Electric Me

    The Electric Me Go Speed Go!

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    I'll be interested in the answers given to this thread.

    My detached answer is I don't think I'd worry too much. My understanding is the Prius system is designed to keep the traction battery constantly in a "range" between charged and discharged. This does happen automatically. But I don't think your gauge or the display is really showing a reality based "complete" picture of where the battery is as far as charge, but designed to show "operational" levels of charge. In other words, the display when showing fully charged isn't really fully charged, so the battery really is never as "full" as you think, nor is probably as low as you think. I can't remember the percentage range the battery is suppose to remain within, but I know a range exists.

    But I admit I'm NOT the person for this answer, the experts will have better indepth feedback.

    I'm honestly curious as to the answers to your questions. My uneductated guess is you don't have a problem. Despite your using the dynamics of a specific driving enviroment and trip to "overcharge" the battery on the one Prius, look at it this way, even in this case, you wouldn't probably perceive it as a problem if you did not have another Prius inwhich to compare battery charge behavior. The behavior of a battery pack is not going to be 100% uniform and static from one Prius to another.

    But clearly...as for many of you-all the time, don't listen to me...I'll concede that there are others more technically versed for a better specific answer...and I'm as curious as anyone to hear it.
     
  5. David Beale

    David Beale Senior Member

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    You may have slightly changed your driving style, hence you now get 8 bars. In the right road circumstances it's not impossible to get 8 bars consistently. We learn slowly how to drive economically, so that may be why you now find it easy to get the eight bars. It has also been claimed that NiMH batteries, once exercised, tend to work better. This may also contribute to making it easier to get 8 bars (the battery might charge more efficiently). I haven't seen measurements to back this up, but I have noticed they do work "better" after a few cycles of use.

    FULLY CHARGING the battery (you have not done this) will put the battery in danger of overcharging one or more cells (the ones with the lowest capacity fully charge first). This is why Toyota avoids it. Overcharging would put the cell in danger of loosing electrolyte, lowering the capacity of that cell even further. It's a run-away situation so Toyota avoids it vigorously.

    You -should- notice the system trying to dump battery charge (switching off the engine fuel earlier, using MG2 to just spin the engine for no apparent reason etc) when you see 8 bars.

    And just to repeat what has already been posted, you HAVE NOT overcharged your battery or damaged it in any way. You -have- reached 80% charge with 8 bars shown. The HSD will not let it get much higher than that. It will dump the charge as above.

    So it's probably an indication of a "good thing" (tm). Your battery is now working better than ever.
     
  6. qbee42

    qbee42 My other car is a boat

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    1) The battery SOC is fully controlled by the Prius; you can't overcharge or overuse it.

    2) The battery display bars are non-linear. It's harder to fill the last bar. Filling the last bar once doesn't make it any easier to fill a second time. As to why this may appear to be true, people see all sorts of associations that don't really exist. Ever notice how some clouds look like bunny rabbits?

    On an older Prius (not your new 2010), the HV battery will show more willingness to swing up and down in SOC. This is because as the battery slowly wears out it loses capacity. Essentially each bar will represent less stored energy as the battery ages. Once again, this is not what is happening with your new Prius, so don't sweat it.

    Tom
     
  7. Scaurex

    Scaurex Junior Member

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    Thanks for your answers and wisdom guys, much appreciated.


    I do see the fuel consumption display/engine "bump to life" while coasting down hills sometimes, it only stays about 1/4 of the "Liters per 100" consumption display for about 10 seconds and then turns off. (it works opposite of the MPG display, all the way to the top means i'm using 10+ Liters per 100km and for USA its 100+mpg)
    But i can't tell if the engine is actually running, or it's a downshifting/drag procedure...or something else?


    I didn't realize that "full" on the display was only 80%. I don't think i have completely charged the 8th bar until the charging system turns off. I've done it once to a rental Prius before we bought our cars; I was using the brakes slightly for resistance on down grades in the mountains, the battery had shown full for a while. Then the charge indicator on the display disappeared, and the brakes were calipers only. I had to use "B" for engine braking resistance, the engine droning noise at highway speeds in "B" is quite loud and grows tiresome quickly. Glad i don't have to use that option regularly.

    I was a bit concerned because the cruise control didn't let our second car charge beyond the 6th or 7th bar, so i wondered if this was the computer controlling the amount of charge that "should" be in the battery. It is hard to watch the display while the radar cruise is on, you have to keep pushing display on the steering wheel to see what is happening and it only stays showing for 10 or 15 seconds before it goes back to the radar cruise display...PITA!
     
  8. GrumpyCabbie

    GrumpyCabbie Senior Member

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    I go down a long steep hill pretty much every day and once or twice the battery has become so overcharged that it has actually switched off charging and just used the friction brakes. It has only happened once or twice and I don't worry about it - yet.

    I assume if it were to overcharge a couple times a day like this then the battery life may be reduced, but as yet I'm not too concerned.
     
  9. austingreen

    austingreen Senior Member

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    1) yes there is such a thing as too much charging. The only way you would be able to do it is if the charge management is not set correctly. The gauge we have is not representative, and toyota tries to manage SOC of 40%-80%. I'm curious from the experts if 8 bars is 80% and 2 bars 40%. There should be no problem going outside of this state of charge for short periods of time.

    2) Toyota has worked a long time to figure out the states of charge for longevity of the battery.

    3) Is it sticking at 8 bars, or is it only a short time before it goes down to 7. Its doubtful that this has done damage. There has not been enough time out for these batteries to know exactly what will kill them. For gen I heat seemed to be the biggest killer, but there should have been improvements.

    4) I have no clue. I seemed to hit 8 bars with normal temperatures, but now with lots of ac I don't seem to be hitting it. It could be something about your driving habits, or something to do with breaking in the battery.
     
  10. MJFrog

    MJFrog Active Member

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    I can only speak for a GEN II, but the GEN III is probably similar. Using my ScangaugeII I see 8 bars green at 75% SOC. I know for a fact that any particular bar will go on at a certain percentage on the way up, and off at a lower percentage on the way down. I don't have the exact numbers, but I've seen a chart posted here on PC...probably by Hobbit or efusco (or possibly someone else).

    I've seen the Scangauge register as much as 80.5 SOC before the ICE would trigger to come on and 'waste' some charge.
     
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  11. energyandair

    energyandair Active Member

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    If the car is behaving normally it should protect the battery, just as others have said.

    If your commute finishes with a downhill run in both directions then I would expect to have a high state of charge at each end of the commute.


    Note that all of this advice is based on normal behaviour.


    What you have described however, does not sound like normal behavior to me. Specifically:
    • Operating consistently between 6 & 8 bars is not normal
    • Operating under the same circumstances in a manner that is very different from past behaviour is not normal
    • Operating in a very different manner from your other Prius is not normal (assuming that they are both Gen 3)
    If it is not behaving normally then the consequences will depend upon exactly what is different. Some faults may be benign. Others may have significant consequences.

    If it were mine, I would write down the symptoms as clearly as I could, double check that my description clearly and accurately described was happening and why it concerned me, then notify the dealer and and ask them to sort it out.
     
  12. Rokeby

    Rokeby Member

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    Here you go:

    [​IMG]
     
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  13. Skoorbmax

    Skoorbmax Senior Member

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    I wouldn't worry about it.
     
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