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Battery Tender/Charger Questions

Discussion in 'Gen II Prius Technical Discussion' started by bdifr78, Apr 17, 2012.

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  1. bdifr78

    bdifr78 New Member

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    Hi Everyone,

    Sorry for the dumbish question. I read several threads and still don't have any good answers for my questions.

    Just bought my 08 prius a few weeks ago. When I went to test drive the car it was almost fully discharged. The sales person had the car on and running before we got there and said it needed a few minutes prior to driving it. This was well before I knew about the differences between a typical car 12v and the prius 12v. So very quickly after getting on PC I started reading all of these threads bout the 12v, it's relative short life and all of the problems that can be attributed to it. When I tested my battery using the internal check recommended on other threads it did appear my battery is on the lower side of things. When I first tested it was giving me 11.8v on the first testing reading.

    I figured that the battery had a bit of time left on it but I'd rather replace with the Optima then wait until the OEM dies on me at an inconvenient time. So with the recent amazing deal on the Optima I just bought one. The more I read about the battery health/life of the Prius 12v the more often I am testing my battery. The weather is getting warmer here to and I have been driving the vehicle more and more, so a few days ago my initial reading was 12.1 and this morning 12.3. All of these readings are in the morning after the car has been sitting overnight.

    I am not that mechanical but think I am going to take a stab at installing the optima myself. However it might be a while before I get around to that, especially as it seems my current battery is healthier than I thought it was. So I would like to get a battery tender/charger to keep the Optima healthy as it sits on the shelf and to get it up to a full charge before installing it. I would also like to use one to take my current OEM battery up to full charge and drive it for a week or so after that to see how it is doing.

    I was hoping for suggestions on battery tenders/chargers. Is the battery tender junior that some recommend good enough for my needs?
    http://www.amazon.com/dp/product/B000CITK8S?tag=priuschatcom-20 about something like this that I can pick up easily at my local Advance Auto Parts?
    http://www.amazon.com/dp/product/B0009IBJAS?tag=priuschatcom-20 question is kind of the dumb one. I live in a condo and don't have access to a 120V AC plug where I park my car. Do all of these battery chargers/tenders need to be plugged into the wall while charging or can they be charged up and then taken out to the car where I would hook them up to the current battery to get it up to a full charge? After I install the Optima I plan to maintain it by bringing it up to a full charge once a month or so to compensate for my frequent short trips.

    Thanks.
  2. edthefox5

    edthefox5 Senior Member

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    Howdy,
    First of all your battery is done. You can charge it to keep it going but that battery will start killing your mileage because of its inablility to charge fully. And if it dies on you on the road be really careful when you jump it. Correct polarity up front jump points and donor car OFF.
    A reverse polarity jump can total out a Prius in electrical repair costs.

    And no have not seen a battery powered charger myself. There's solar tenders out there though but they take forever.

    FYI: Battery tenders are ok but your missing the most important part and thats a meter to tell you exactly how much current its pulling upon start up of charge. I see the one has LED's but I want more accuracy because that will be the best check of battery health.

    Once a month I hook up my standard battery charger with 2 AMP MODE. I notice how much current it pulls upon hook up of cahrge cables. Usually around 5 to 6 amps. Your failing battery will be much more.

    Then exactly how long it takes to reach full charge (0 current draw on meter). For me thats about 15 minutes.
    Thats the most important part...time and if it becomes fully charged.
    A bad battery thats sulphated will never reach full charge.

    But its good to have both a tender and a regular charger. Tender if you know you won't be driving the car for a while and reg charger to do instant maintain & check. But that won't work for you. There's no place you know that every few days you can get a plug in for 15 minutes? Work?

    The prius battery is not that bad if you take care of it. I'm on the original on my 07.
  3. Britprius

    Britprius Senior Member

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    There's something wrong with your battery charger if in the 2AMP mode it us putting out 5 to 6AMPs. The OEM Prius battery should not be charged above 4AMPs as stated on it's label.

    The 12v battery can only seriously affect fuel consumption if it has one or more shorted cells, sulphated batteries will appear to charge quickly but will have very little amp/hr capacity.

    Charging the battery for 15 minutes at it's maximum charge rate will only add less than 1amp/hr to it's capacity of 45amp/hr better than nothing I agree but not worth the effort.

    The OP's battery does not seem to be to bad, a little early to tell as he says that the last reading after sitting all night was 12.3v not to bad and may pick up further.

    The best action would be to fully charge the battery and then make an assessment of it's condition. A battery that is discharged is exactly that, not a piece of scrap.
  4. cnschult

    cnschult Active Member

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    when my 12V Denso was dying I was trickle charging it every night while awaiting my Optima (see my post about getting one for under $125 shipped to your door!!!)

    I have a microprocessor controlled Black & Decker VEC1095ABD, maybe $70 at walmart and has settings for different batteries (wet, gel, AGM), power (2,10,25,75 amps), a battery reconditioning desulfate mode, voltage and alternator check.

    As I said my DENSO was dying so when I hooked it up at 2.0amp setting overnight it would run at 2.7amps for a few hours, than 1.9 until it shut off automatically when the DENSO was full. Whatever setting my charger is at it always ran above that amperage at start, maybe that's industry standard but its never given me a problem at 2.7amps, I have no idea why a 2amp setting would yield 5 or 6 amps from the charger, the slowest and lowest charging setting is always best for any battery, even when I charge my corolla which has a more robust 35-series battery than the prius I still use a 2amp setting overnight.
  5. edthefox5

    edthefox5 Senior Member

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    Thats what I'm trying to do. Stick to dangerous oils and greases.
  6. David Beale

    David Beale Senior Member

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    I purchased the larger "Battery Tender" (it's a trademark name). It's designed to be left on a motorcycle battery over the entire winter. Mine puts out 2 Amps as I recall (it's in the garage, awaiting need of use). It's a metal chassis/box with leads.

    They all need to be plugged in to use.

    If you go on a "long drive" (perhaps four hours or more of driving, with stops in between is ok) the Prius battery will charge up quite nicely. Even just driving in the city for the same time does it. The car just has to be "ready" for the charge time to be effective.
  7. M8s

    M8s Retired and Lovin' It

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    We have two homes and leave a car at each so that we only need to drive one car back and forth. As a result, we always have one car on a battery minder.

    I bought an Optima 3+ for one home and an Optima 4 for the other. They're about $50 each at Amazon. I've used each for over 5 years and they still work like new, even though they are plugged in for 6 months per year.
  8. Constance83

    Constance83 New Member

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    [​IMG]First of all your battery is done.
  9. 99009903

    99009903 New Member

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    I put a meter on the 12 v connections in the engine compartment with the car not turned on. Readind was 12.1 volts. I pushed the start button and the voltage jumped to 13.8v. I assume this means the battery is charging...without driving the car...right.

    Thanks, richard
  10. David Beale

    David Beale Senior Member

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    The inverter has a battery "eliminator/charger" built into it. With the car off you will measure the voltage at the battery. When you turn it on you measure the voltage the invertor circuit puts out. It's nominally 13.8V, and if that is what you measure, your battery is -probably- good. It's not a sure thing, but I've observed that a discharged battery (even a bit) will cause the system voltage to rise slightly (to perhaps 13.9 to 14.2). There is no charge control on this system, it's called "float charging".

    But yes, when the car is "ready" the battery will be float charged. Engine running or not, car driving or not. It's powered by the "traction battery", and if it gets low enough the engine will run to charge it back up.
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