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how to properly charge the 12V battery

Discussion in 'Gen II Prius Care, Maintenance and Troubleshooting' started by cnschult, Mar 9, 2012.

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  1. cnschult

    cnschult Active Member

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    I swear I've read all the usual noob posts and done all the searches and can't find the answer, most threads are warnings about not letting idiots jump start the car or warn you not to jump start other cars or tell the OP to just buy a new 12V battery. I have a Black & Decker battery charger that I want to use once a month on the Prius just for good PM, it has these settings:

    2amp (float or trickle, obviously this is the one I'll use)
    10amp (normal charging)
    25amp (heavy charging)
    75amp (jump starting)

    1. Wet are these settings useful
    2. Gell or just a marketing gimmick?
    3, AGM I use this setting for oem, right? what about the opima?

    Battery Recondition (Is this DeSulfate mode good for the Prius 12V battery as well??? what about a 'normal' car?)

    Voltage Check (I'll use the maintenance mode myself, but if you hold this button it does an alternator check, again, is this for the Prius? how about a 'normal' car?)

    How to you maintain the 12V battery? do you:
    a. charge under the hood, if so where do you put the negative clip?
    b. charge in the trunk, without removing negative cable
    c. charge in the truck, after removing the negative cable
    d. remove battery and charge in the house (very inconvenient!!!!)

    I assume the Prius should also be fully powered OFF while charging, let me know otherwise. If you recommend trunk charging, can the hatch be left open or should the cord be run through an opened window?

    I hope someone knowledgeable answers these questions, and what is the proper way to jump start a Prius with A) another vehicle and B) my battery charger (do I use the 75amp setting? or not)

    thanks in advance
  2. qbee42

    qbee42 My other car is a boat

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    Use the low setting (float). You can charge from under the hood as long as you have a decent charger. If you have an old POS I would disconnect the battery to protect all of the electronics. If you need to desulphate a battery, make sure to disconnect it. The higher voltage could be bad for the electronics.

    As to the type setting, match it to your battery.

    Here is the system I like to use:

    [​IMG]


    Tom
  3. jbrad4

    jbrad4 Active Member

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    You should not need to do anything to your battery as long as you are driving the car regularly. The car will charge it. If the car is not charging the 12v battery, you either need a new 12v battery or your car's charging circuitry needs to be repaired. I would not be putting a charger on it on a regular basis.

    The Optima Yellow Top battery is AGM (Absorbed Glass Mat).
  4. arewethereyet

    arewethereyet New Member

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    I've seen advice saying that folks sometimes don't drive enough to charge their battery. One person said they drove every day about 20 minutes each way and they were told they didn't drive enough.

    I drive 40 minutes a day and I've been told I drive enough to keep my batteries charged which contradicts the above statement.

    Does anyone have data/testing to back up either argument?

    Thanks
  5. cnschult

    cnschult Active Member

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    yes I drive fairly short trips
    no I don't think my 12V battery needs to be charged (no symptoms yet, but keeping fingers crossed), I just figured what the heck, I've got the charger anyways, mind as well get some use out of it.

    20 minutes is plenty enough to charge the 12V battery back up again, but that's me, I don't have heated seats, I don't run HVAC or defroster unless absolutely necessary, i don't have an amp & subs, the more stuff you are running the less juice the car is sending to recharge the battery and the longer you need to drive to charge it back up.

    Stating how long you need to drive is like the epa stating how many mpg you will get on the window sticker, read the fine print and you will see they give a range for both city and highway mileage because driving style, air temperature, terrain, tires & vehicle maintenance all play a factor in your mpg.
  6. edthefox5

    edthefox5 Senior Member

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    I do and have done so for all my cars for many years. Its good to put a charger on the car and bring a car battery to max charge once in a while.
    And at the least you can monitor charge rate over the battery's life and see how long it takes to go to full charge. If it suddenly starts taking much longer to reach max charge it gives you a good heads up the battery is getting sulphated or worn out you would never notice otherwise till you go to start the car and its dead.
    That scenario times a thousand here at PC. Because no one ever puts a charger on there car and really have no idea what condition the battery is in tll it leaves them. And then its jumper cable time.
    No thanks. I'll take 10 minutes a month and check my battery.

    I am still on my original AGM and going pretty good. But I can tell it has about 6 months before it starts scaring me.

    I haven't had to buy a car battery in over 30 years.
  7. fuzzy1

    fuzzy1 Senior Member

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    Does this mean your Prius has a battery more than 30 years old, that started its life in another vehicle?

    If you meant something else, then how long do you keep cars that haven't needed battery replacements? My household's oldest functioning batteries, a pair of marine gel cells in a hobby-sized solar system, are 18 years old. They are not as old as the household's oldest cars (one 23 years now, a previous one disposed of at the same age). While they have sufficient remaining capacity for their current use driving evening LEDs I don't believe they have enough left to handle a car's needs.
  8. edthefox5

    edthefox5 Senior Member

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    No it means that I never had to replace any of the batteries in any of the cars I have owned in the last 30 years maybe more as I maintain them. Like I said in my post I am on the factory original battery in my 07.

    Replacing a car battery is a dangerous hassle. I would like to avoid handling it at all costs.
    Its much easier to maintain it with an outboard charge and that will tell me its health too. That takes about 10 minutes once a month. Increased interval if I'm concerned about a battery.
    And with the Prius if I know I won't be using the car for more than 2 days I will throw a float charger on it.
  9. fuzzy1

    fuzzy1 Senior Member

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    But ... but ... but ... how long did you keep those cars? Could the 15, 23 (current), and 23 (past) year old cars in my household still be on their OEM batteries with your maintenance schedule?

    Your '07 car being on its original battery fits well with our past non-hybrids, which have needed replacements between 7 and 9 years. (This is a comparatively mild climate.) Having the Prius' battery fail earlier will be a new experience for me.
  10. cnschult

    cnschult Active Member

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    i'm still waiting for someone knowledgeable to explain the proper and safe way to charge the prius 12V battery. Almost none of the questions in my original post have been answered, lets not get into a pissing contest to see who can get their batteries to last longer than the other.

    as for edthefox, I'm assuming you have added water to all your previous batteries and not just occasionally charged them. Well adding water to the prius 12V battery is very difficult as you have to drill holes and is inherently very dangerous. Whereas I do applaud your desire to make your oem battery last as long as possible, (that is basically the point of this thread) I do hope you will replace the 12V battery with an optima when your 12V starts to give signs of dying.
  11. uart

    uart Senior Member

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    - For a regular (non pulsed) charger just charge at the front jump terminal.

    - Connected the negative to any shiny (non painted) bolt head that bolts into the chassis. I've found a few of them in the engine bay not too far from the jump terminal.

    - Charge in AGM mode @ 2A max float-trickle mode.

    - Minimum time is not really known without knowing the initial state of charge, but 8 to 10 hours should be plenty.

    Personally I think 40 mins driving per day is probably enough to keep the battery in reasonable condition without requiring any extra charging.

    My only concern would be that if your charger is a little more aggressive than the Prius inbuilt charging system then over time it may deplete the water in the battery. So, given that you're never topping this off, regular charging may actually result in a shorter service life rather than extending it.

    BTW. It is a bit of a pain, but you can top off the water in the battery without drilling anything out. You can access the filler holes by removing the label from the top of the battery and prying off a plastic cover. You do have to remove the battery from the car though.
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  12. fuzzy1

    fuzzy1 Senior Member

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    I thought they were covered very well in the very first reply.
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  13. Patrick Wong

    Patrick Wong DIY Enthusiast

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    A ) Make certain that the jump cables are correctly connected, positive to positive and negative to negative (or ground). If you use the dedicated positive jump start terminal in the main relay/fuse box you may find that a jump cable with substantial current carrying capacity has a spring-loaded clamp that is so large it won't easily connect to the small tab provided in the jump start terminal. In that case you would have to improvise some means such as use of a large paper clip or an alligator clip to bridge between the two.

    Leave the other vehicle turned off while you are hooking up the cables and jump starting. Then make the Prius READY, disconnect the jump cables, and you are done.

    B ) NEVER use the 75A charger setting on the Prius battery unless you really want to risk damage to the battery and the vehicle electronics. In order to get 75A to flow, the charger produces a very high voltage.

    Regarding periodic battery charging, I think that is a great idea and do that at least 2x per month on my vehicles that are lightly driven. I also agree that you need to allow substantial time for the charge to complete, not knowing what initial charge the battery has.

    My personal practice is to use a lab power supply which has 3A maximum current capacity, set to 13.8V, to charge the 2007 Prius battery. I keep an eye on the current flow, and am done when the current drops down to 0.1A or so. At that point the current flow has stabilized and will not continue to decline.

    It takes several hours for the current to drop down to that level, although that car logs substantially more miles/month than the others in my household and the battery is only a couple of years old.
  14. cnschult

    cnschult Active Member

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    thanks Patrick, you know I almost put in my OP "can PatrickWong or someone of equal technical knowledge respond only"



    questions not answered thus far: :p

    what setting to use for the oem battery? (someone said optima was agm, but since i've read other posts about people adding water to oem battery it makes me want to use the wet setting, but UART said to use the agm setting, so I am in need of clarification)

    is desulfate good for the prius battery? (someone did mention to remove the battery from trunk to perform this operation, I assume this is okay for the 12V battery if you want to go through the hassle but is this necessary for an optima battery?)

    is using the alternator check a way to check the prius alternator? (does the prius even have an alternator? half a decade I've never seen the word alternator mentioned on priuschat)

    should I disconnect the negative cable just to play it safe, even when charging under the hood? (a few minutes work to save potentially $thousands in damage is worth it for me)

    should windows be cracked so any extra gases produced during charging be able to exit?

    I am happy to patiently wait for an expert to respond :D
  15. alanh

    alanh Active Member

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    No, the Pruis does not have an alternator. It has an electronic inverter that converts the high voltage down to 12v for the battery and 12v accessories.

    Whenever the car is in "ready" mode, the inverter is online and powering the 12v bus. There's no drain on the battery.

    The 12v battery is only used for booting the car computers when you press the start button, and running the 12v accessories when the car is off. It doesn't have to crank the engine like a conventional car. As long as you're not making heavy use of it with the car off, it has a pretty easy life.

    It should just take a few minutes for the small amount of charge used to start the car to be replaced. There's also a small drain for the keyless entry system.

    The battery has a vent tube that goes outside, so if that's undisturbed you don't need other venting.
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  16. fuzzy1

    fuzzy1 Senior Member

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    Use the 2A float setting, as gbee mentioned. My manual lists a max charge current of 4.x amps, someone else with higher model found 5.x amps, consistent with a heavier battery for additional factory features. Both these are far below your next-lowest 10A setting. Patrick's 3A power supply is consistent with these limits.

    Everything I've seen in PC, long before qbee's reply, is that the optima is the same agm type as the OEM unit. The OEM is not wet due to its mounting location inside the passenger envelope.


    The 'alternator' here is a combination of MG1, the traction battery, and HV and 12 inverters, completely different from what common 12V chargers expect. Don't even think of using it.


    I seem to remember the manual saying to remove the battery from the vehicle. I didn't when using the 2A setting to top off mine, but you must make your own choice.
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  17. qbee42

    qbee42 My other car is a boat

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    If you want specific advice you need to provide specific details. You never stated what type of 12V battery is in your Prius. Lacking that, we can only provide general advice.

    Tom
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  18. cnschult

    cnschult Active Member

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    I asked for the charging procedure for both oem and an optima, since I have oem now and soon will be upgrading to an optima I didn't want to have to repeat the thread years from now if we could get all the necessary info out into the open now.
  19. Britprius

    Britprius Senior Member

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    On Prius OEM battery use 2amp setting, on Optima you can use 10amp setting as they say it may be charged slightly higher than that, but slower is better. Pulse charging can be used on both batteries, but not while connected to the car as these chargers often put out high voltage spikes not good for the Prius electronics.
  20. qbee42

    qbee42 My other car is a boat

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    I didn't see it; certainly not in your OP. I suspect the question was clear in your mind, but never made it to print.

    Tom
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