Auxiliary Battery Charging

[green4evr2003]

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

[green4evr2003]

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

[Jonathan]

Maybe a trickle charger to the small 12v batt in the 'trunk'..?

[Frank Hudon]

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.

[Ruudh]

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.

[Patrick Wong]

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.

[magruder]

Hey Patrick,

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

Regards,
Dave

[Patrick Wong]

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.

[magruder]

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.

[richard schumacher]

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.)