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    green4evr2003 New Member

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    I know this has been posted on the Yahoo page before but I had not gained access to the auxiliary battery before now. Where is the best place (and what is the best method) to connect a floating charge battery charger to keep the 12-volt auxiliary battery fully charged while I'm on a 3-week vacation?

    Bruce Webster
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    green4evr2003 New Member

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    Let's see if I can liven up the plethora of replies that this posting has generated. There have been no replies to this since I posted it on Feb. 27.

    Where is the best place and what is the best method for keeping the Prius' 12-volt auxiliary battery charged with a floating battery during long periods of inactivity?

    Bruce Webste
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    Jonathan New Member

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    Maybe a trickle charger to the small 12v batt in the 'trunk'..?
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    Frank Hudon Senior Member

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    I agree on the Classic the best thing to do is connect a small floating charger to the battery terminals in the trunk. I just went thru the Classic NCF and didn't see anywhere that you could do it under the hood. On the new P there is a connector in the fuse box where you can hookup a booster battery to start the car if it has a dead battery and that would be the best spot to put a floating charger on the new ones.
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    Ruudh Junior Member

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    I have wanted a Prius for over 5 years now, in love with the Prius hybrid technology. So this month we bought our "trial" Prius. I wanted a two year old Package 2, but my wife likes the bells and whistles, so since this will be primarily her car, we settled on a very low mileage 2005 Package 6 Prius, metallic Jade green (looks grey to me).
    I've studied the numerous posts on the auxiliary battery issues, especially since we ran ours down the first evening trying to program all her bells and whistles (navigation system, bluetooth phonebook etc). I charged the battery directly in the right rear of the car to restore it, but since then have read some posts that suggest I shouldn't charge it unless it is disconnected from the car's electrical system, since voltage fluctuations might damage some ECUs.
    Is that true ?, comments are appreciated. If true, and I disconnect the auxiliary battery for charging (or replacement), I understand that I will lose some presets, such as the audio system radio stations. I can live with that, but is that all?. Will I lose such things as the bluetooth phonebook, or navigation system Points of Interest (POIs)??
    Love the car.
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    Patrick Wong DIY Enthusiast

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    Congratulations on your purchase. Sounds like you have the Tideland Pearl color. I'm not sure whether you will lose phonebook or nav data when you disconnect the 12V battery.

    Regarding 12V auxiliary battery charging, it is true that Toyota's advice is that the battery should be removed from the car before it is charged. This is ultra conservative advice which is justified because from time to time, it is possible for a battery to explode or have some other problem while being charged. It is also possible for a charger to work incorrectly and provide excess voltage, which would potentially damage the ECUs.

    I personally have confidence in the 12V charger that I use, and periodically monitor the output voltage to satisfy myself that the charger is working properly. Hence I have no problem attaching my charger directly to the 12V battery while it is installed. However if you lack similar confidence in your charger, then you may do well to follow Toyota's advice.

    In any event, be sure to use the low current setting on your charger (i.e., 2A) since the maximum charging current per the warning label on the battery is ~4A. Good luck.
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    magruder Average Member

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    Hey Patrick,

    I thought you had to use a special charger for an agm battery. Apparently that is not correct?

    Regards,
    Dave
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    Patrick Wong DIY Enthusiast

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    Hi Dave,

    It is true that the Toyota TSB on this issue suggests using only their approved charger, and the TSB also suggests charging at 10A is OK when this equipment is used. Since it is not reasonable to expect owners to purchase this charger for DIY work, I suggest using the 2A current setting, then no harm will be done.
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    magruder Average Member

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    I see, thanks for the info. I guess the AGM specialized chargers work in such a way as to limit the amount of electrolyte burnoff, while still charging at 10A. I personally have not charged my battery yet, but I drive the prius almost every day.
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    richard schumacher shortbus driver

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    On the other hand, a four-year-old battery that has been completely drained probably doesn't have a lot of life left in it. It might be less bother overall to simply have a dealer replace it. (There is no known direct aftermarket replacement for the battery. They all require some adaptations or an adapter kit.)

    Unless you are parked in a completely enclosed space with no ventilation, if you want to use any accessories I suggest leaving the car on ("Ready") as though you were about to drive it away, and in "Park", instead of using ACC or IG-ON. That way the car will start the engine as needed and manage battery charge all by itself as it was designed to do. (*Don't* leave it "N" for any length of time; it cannot charge the big traction battery in "N", and if that drains it would be a big problem.)
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    jayman Senior Member

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    I've posted in other threads that I hook my VDC Battery Minder directly to the aux battery. Have been doing so four years now, with good results. I believe it offers extra safety to the car if you use a "smart" battery charger/tender with automatic float charge control, and reverse polarity protection
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    Ruudh Junior Member

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    OK, I agree that probably I will need to replace the 12 volt aux battery in our 2005 Prius. But as I said before, I don't relish the prospect of having to reprogram all the presets, including the Navigation memory points, and especially the two bluetooth phonebooks. So here is a temporary fix, which I may leave in even after I replace the battery for trickle charging during proglonged non-use.

    I installed a flat, molded connector across the positive battery terminal clamp and the ground connection at the chassis. The flat connector is then routed between the wall of the car and the carpeted right floor insert. This provides two basic functions:

    1. If I want to trickle charge the battery, I don't have to disassemble the hatchback area to get to it. All I do is connect up the matching molded (and polarity keyed) connector from my charger (1.5 amps) to the aux battery connector. Tested it, works fine.

    2. When I do battery maintenance, whether it is cleaning connections or removing and replacing the aux battery in the near future, I can safely do so without fear of losing any presets after I connect a small sealed 12 Volt battery to the connector. The one I have is a 7.5 Ah sealed rechargeable lead acid battery. 7.5 Ah is overkill, there are smaller batteries like 12V1.2 AH out there that will do just fine.

    The molded connector sticks out about 1" above the cargo floor, and you won't see it unless you're looking for it. I took some photos of the installation and tried to insert them here but I guess Priuschat only accepts links to another site where the images are available. Didn't know that, I'm a newcomer to this site.
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    jayman Senior Member

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    I'm pretty sure you need 5 posts minimum before photos are allowed, or links to a site like Photobucket
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    tochatihu Senior Member

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    Thanks for the description ruudh, it sounds like a very useful addition. Just post some worthless stuff in Fred's (like the rest of us do :) to get your post count up, then you can attach the images.
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    jayman Senior Member

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    Just make a few posts about sheep. Trust me, thats a *great* way to get the post count up, and make a lot of the more "normal" PriusChat members wonder if you're deranged
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    GregP507 Junior Member

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    I was a bit surprised when my Prius Plug-in had a dead aux battery in the showroom at the dealership. I would have expected at the very least, that the main HV battery would have some sort of interconnect to prevent the 12V aux battery from going dead. As it was, they had to boost the aux battery to get the car to start up. I can't see why the system can't sense when the 12V aux battery is running low, that it can't shunt over some of that 4.4 kilowatts of stored energy, which is just sitting there in the main HV battery.
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    GregP507 Junior Member

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    If your PIP is like mine, there is a boosting terminal under the hood in the main fusebox. That seems like a better place to put a battery maintainer.

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