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Discussion Starter #1
I'm leaving my 2004 #9 Prius unattended for 10 weeks and was researching an alternative to disconnecting the auxiliary 12volt battery (e.g., connecting a 2 amp trickle charger). I understand that I should turn off SE. I don't even have to lock the doors (it will be locked in a garage). I assumed all would be well. However, I called Toyota (national) and in the course of a one hour conversation with an "expert" (who had to continuously access the internet and other "experts") I was told the following:

I can use a 2 amp trickle charge to keep the auxiliary battery charged (thereby eliminating the need to return and reset the radio and any other memory settings... navigational and otherwise).

But... the car must be started and run for at least 30 minutes once every 50-60 days or the MAIN battery will fail and will cost a fortune to replace.

I told him I'd never heard this before. He said it was a recent bulletin on Toyota's internal message board. I said any failure of the main battery caused by storage must be covered by warranty. He said it wasn't. I said, as an owner I'd never received notice of this problem, it's not in the manual. He referred me to the Toyota web page and a list of faq's:

"In addition to the storage tips for our conventionally-powered vehicles, our hybrids require additional steps for each battery, as the hybrid vehicle battery and auxiliary battery will discharge and their condition is liable to decline.

To prevent excessive auxiliary battery drainage, charge the battery at least once every two weeks by driving the vehicle for 15 - 20 minutes with all non-essential electrical accessories (such as air conditioning and audio equipment) turned off. As an alternative, you may disconnect the negative terminal of the auxiliary battery.

For the hybrid vehicle battery, charge the battery at least once every two months by starting the hybrid system for about 30 minutes *. Check that the "ready" light is on and all lights and electrical accessories are off. It is not necessary to drive the vehicle, but do not start the hybrid system in an enclosed area unless the tail pipe is connected to an exhaust hose to prevent harmful build up of fumes."

I am leaving the country in two days. I am more than happy to disconnect the 12v auxiliary battery and deal with reprogramming the radio when I return. I do not, however, want to return to a dead main battery. Has anybody out there left their Prius unattended for 10 weeks and had problems starting up on their return?[/i]
 

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Well, the Toyota guy said 50-60 days, and by my math, you'll only be gone 70. If you can find a way to drive around in such a way as to leave your hybrid system battery full (green 8 bars on the display,) you should be fine. For that matter, I have to imagine that (like with most engineer-to-technical-writer decisions,) that 50-60 days is under a 'worst-case' scenario, such as the middle of winter, with the battery starting out at 2 bars.

You'll be fine. And if not, well, take it to a different dealership than the one you called, and claim it was only sitting for a week.
 

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I cannot believe that allowing a NiMH battery to discharge completely would ruin it. While maintaining it always within a narrow range of charge extends its life, NiMH batteries are used in many deep-discharge applications, and a single event of discharge should be insignificant. The worst-case would be you'd have to have it towed to the dealership to be re-charged.

And as ehurtly says, they're most likely going by a worst-case scenario: car parked with 2 bars SOC and left 60 days. You'll never be able to park yours with 8 bars unless you live at the bottom of a big hill, but you can manage 6 bars, and you should be fine for 70 days.

How to assure you charge the HV battery to 6 or 7 bars: Start it cold and take a short drive, of a mile or two. If it goes into full hybrid operation (where you see the ICE stop delivering power and all power coming from the battery) your trip was too long. If necessary, let the car cool off completely and take another short trip. You should be able to park your car with 6 bars SOC and be well outside the worst case.
 

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I suspect that Toyota is being overly cautious. However, if it were me, I'd ask a friend or neighbor to power it up a time or two while I was gone.
Good luck,
Moo :)
 

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Discussion Starter #6
My trip was delayed, so I had lots of time to try to solve the problem of Prius storage. All indications assure me that the hybrid battery, if parked almost fully charged (at least one bar into the green, not hard to accomplish) will last 6 months or more without risk. The auxiliary battery, as we all have been warned, can discharge in a matter of days and certainly within 2-3 weeks. We are advised to disconnect the ground strap (not an easy task - just getting to the battery is a bit of a pain) and return to a car that needs many of its settings re-set (e.g., radio, navigation memory) and some lost forever (e.g. trip odometers). A solar charger has been suggested, but not everybody can park their car in sunlight and not everywhere has enough sunlight to keep the battery charged. The simple solution is to hook up a Battery Tender Jr. I stress the "Jr." because it charges at a rate of 750mAmps rather than the 1.5-2 Amps suggested by Toyota and common to many "trickle charge" units. Higher amperage runs the risk of overcharging your battery (a worse fate than returning to a dead battery). I attached the harness of the battery tender to the positive post on the battery and bolted the negative terminal to the floor of the trunk using a metal screw already attached near the spare tire. I fed the harness up along the edge of the carpeting in the rear storage compartment so its connector sits in the corner of the "trunk". The battery tender simply plugs into this connector, then you plug the tender into a wall outlet. A red light came on, indicating the battery needed charging. I left it 24 hours and found a green light on the tender, indicating the battery was fully charged. This unit turns itself on and off, will not overcharge any battery, and can be left plugged into the vehicle for years (if necessary) at a time. I can attest to that. I use the exact same chargers on two motorcycles and have not bought a new battery for either bike in over 5 years. Why Toyota didn't make this part of the design is beyond me. But, in 15 minutes, and for $35, I have solved the problem of the dreaded dead auxiliary battery. I hope this is helpful to anybody else out there. Of course, for those of you who leave your cars in an airport garage or anywhere else without access to an electrical outlet, this obviously won't work. There are solar chargers that hook up exactly the same way (some with the exact same connector - so once you've hooked up a harness to the battery, it can be used for either type of charger), but you must be certain to buy a solar charger that produces the correct amperage.
 

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Jeff,

I'm glad you found a solution to your quandry about leaving the car for 10 weeks. But I guess I'm confused about the terminology here. Does "auxiliary battery" mean the regular car battery that every car has, as opposed to the hybrid battery whose charge shows up on our MFD? Why would that discharge in a matter of days? No other car I've owned had such a problem.

Susan
04 silver BC
 

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Yes, by "auxiliary battery" he means the 12V battery like those in conventional cars. This can discharge rather quickly because the SE/SS system and computers are always on, with the SE/SS being much the largest load. If the car will be unused for more than a few days Toyota advises turning off the SE/SS system using a button near/under the steering wheel. Consult the owner's manual.
 

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Hmmm. So the battery level indicator on the display is for the hybrid battery only. You would think if the 12V battery is susceptible to quicker discharge than one is typically used to in conventional cars, Toyota could have included a level indicator for the aux battery also.

richard schumacher said:
Yes, by "auxiliary battery" he means the 12V battery like those in conventional cars. This can discharge rather quickly because the SE/SS system and computers are always on, with the SE/SS being much the largest load. If the car will be unused for more than a few days Toyota advises turning off the SE/SS system using a button near/under the steering wheel. Consult the owner's manual.
 

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Discussion Starter #11
long term storage alert

To answer the question about the auxiliary battery: it is indeed the 12v that starts most every other conventional car. However, two things make it different on the Prius. First, it's about the size of a large motorcycle battery and has a small capacity. That's why it will discharge in a matter of a very few weeks, even with SE turned off and the doors left unlocked. Secondly, it is different because the purpose it serves it simply to initiate the hybrid system. It does not power a starter motor (as in standard ICE cars) because the Prius ICE is started by the hybrid battery when needed. Why the auxiliary has such a small capacity and why Toyota chose to stick it in such an inconvenient place is beyond me. But, there is so little to complain about with a Prius, that having found the solution I outlined above has made the car almost perfect. I'll notify the group again in ten weeks when I get back home. Hopefully, I'll unplug the tender and start the car right up.
 

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Well, it's almost like you're all wrong

Okay, maybe not like that, but still....let me tell you my own experience that I've just had
We live in NJ. The car is parked in a garage, underground. When we left, the battery meter showed blue bars - the highest one. (ie the lowest it can get before turning green). We were gone July 9-Aug 25. All we did was turn off the SE/SS by pushing that little buttong under the steering wheel. We locked the doors and left the car. We did not disconnect the auxiliary battery. In addition, I'm not sure why you say that all data would be lost if you did disconnect it. (??)
Anyway, when we returned home, the car started up as if we left just the day before. The battery meter was at the exact same level. The car started up without a glitch - no jump-starting required. Actually, it was quite amazing how gracefully the car "stored" itself for such a long period.
Of course, we weren't gone for even two months. Still, the fact that nothing was changed in that time leads me to believe that the wortst that could happen is that the main battery would discharge slightly. If discharged completely, your Toyota dealer could charge it...in which case it would need to be towed/cost money. In addition, Toyota does say that completely discharging the battery is bad for it (Daniel: this is to answer your ?).
 

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Lensovet, Thanks for your post. BTW, I'm one of the other Prius owners in town. We met in June at the high school. Our sons are friends.

Richard and Jeff: thanks for your replies.

I was starting to really worry that I'd have to figure out how to trickle charge, etc or have problems with the small battery. Lensovet's experience is reassuring and actually makes much more sense than the idea that the battery could discharge that fast without major precautions. Question: If you turn off SS/SE, how does locking the doors rund down the battery??

A possible answer to the question about losing settings when disconneting the 12V battery: Whenever I've replaced a battery in other cars, my radio station presets and clock are wiped out. I wouldn't be surprised if the same thing happened in the Prius, plus losing NAV presets and/or trip odometers. Sound reasonable?

Susan
 

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Locking doors, etc.

Heh....
Susan, I'm actually the son. My dad reads these forums but never posts. Remember, I'm the one that convinced him to buy the car in the first place.
Locking the doors could technically discharge the battery because it activates the anti-theft system. However, apparently 6 weeks isn't enough to discharge the battery that way.

The reason i was questioning the rationale behind losing settings - couldn't the main battery be used for that? Just a thought...

And hi!
 

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Discussion Starter #15
Thanks for relating your storage experience. It seems everybody's experience with the auxiliary battery has been different. Throughout this website, there are countless stories about discharged auxiliary batteries - some in a matter of days. Your 6 weeks without a hitch is an anomaly, but very reassuring at the same time. The settings you WILL lose, should the auxilary battery die, are radio presets, clock, navigation memory (obviously not the DVD with locations and directions, but rather preset locations you have programmed in), and trip odometers (A & B) but not total mileage. It's a pain, though a minor one. It's a bigger pain to take the trunk apart and jumpstart the auxliary battery to start the car. That's why I chose to install a battery tender. It's particularly reassuring to hear about your experience with the hybrid battery (which, by the way, has no connection to the above mentioned memory settings and is not at all in circuit until the car is in "ready" mode). It makes no sense that a battery warrantied for 8 years and 100k+ miles would die in a matter of 6 (or even 10) weeks. But, still, there are numerous reports that it has. Temperature during storage certainly has something to do with the rate of discharge. Because there have been so many varying stories, and Toyota has a warning on its website, I simply chose to take as many precautions as possible. It's a learning process. But, it would have been totally unncessary had Toyota built in ways to obviate our concerns.
 

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jefff12 said:
. . . Your 6 weeks without a hitch is an anomaly, but very reassuring at the same time.
I don't think this is an anomaly. lensovet did take precautions to minimize the drain on the battery. I think people who experience loss of 12V battery charge tend to report that at a much higher rate than people who leave their cars for several weeks but don't have 12V battery problems.

jefff12 said:
. . . It makes no sense that a battery warrantied for 8 years and 100k+ miles would die in a matter of 6 (or even 10) weeks. But, still, there are numerous reports that it has. . . .
The 12V battery is not warranteed for anywhere near that long (3 years maybe?). I have not heard of a single case of the HV battery draining due to 10 weeks+ of normal storage. There has been at least one report of a salvaged Prius with a discharged HV battery, but who knows what happened to the battery in the accident or at the junk yard.
 

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lensovet said:
The reason i was questioning the rationale behind losing settings - couldn't the main battery be used for that? Just a thought...
For safety reasons, and perhaps others as well, the HV battery is completely disconnected from the system when the car is powered off. Thus all those standby kinds of functions, such as alarm and SS/SE must be run off the 12-v. battery. This battery is small because it does not need to crank the engine, but it would have been better to make it large enough to run all that stuff longer.

jefff12 said:
... It's a bigger pain to take the trunk apart and jumpstart the auxliary battery to start the car. That's why I chose to install a battery tender...
The car has "jumpstart" terminals under the hood. I believe you can also connect your trickle charger there.
 

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Daniel said:
The car has "jumpstart" terminals under the hood. I believe you can also connect your trickle charger there.
Thanks for mentioning that! I was wondering about exactly those terminals and whether they could be used instead of digging under the trunk. What are the relative positions of the hybrid battery and the aux battery? Aux under the trunk and hybrid under the back seats? Do I have that right?

Now if I could only find a way to schedule a 3 month trip to somewhere far away . . . Maybe cruise the castles on the Loire, or an extended stay in Tuscany, or join an archeological dig in the mideast. Can't think of any other reason I'd want to leave my Prius behind for that long! :D

Susan
 

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Discussion Starter #19
Three months ago I started this thread after being warned by Toyota that leaving my 2004 Prius parked for 10 weeks would most likely cause the hybrid battery to discharge to a dangerously low level. Toyota advises that the car be started at least once a month to recharge the hybrid battery and that the smaller 12v battery be disconnected between starts because it will not last more than 2 weeks without recharging.

After considering a number of owners' suggestions and doing a little research of my own, I connected a trickle charger (a simple motorcycle trickle charge unit I bought for $30) to the 12v battery. The night before I left, I drove the car, coasting as much as possible, and charged the hybrid battery up to the first green bar level (7 bars). I parked the car in my garage, plugged in the trickle charger, and left town for 10 weeks.

I returned three days ago, unplugged the trickle charger, and the Prius started right up. The display STILL showed 7 green bars for the hybrid battery - as if I'd driven the car just the day before.

For all those concerned about long term storage, follow the simple steps described above. If it's impossible to connect your Prius to AC power and a trickle charger, simply disconnect the 12v battery, but make sure your hybrid battery shows a high charge before leaving it parked.

Toyota's warnings, as advised by other owners, is simply in response to a "worst case scenario" in which the hybrid battery is left with a low charge.

I'm taking more vacations in the future, with no worry about my Prius when I return.
 

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My 2004 owners manual states car can be parked for a year without any extra care being taken with the main battery supply. 12 volt should last several months and car can be easily started as long as there is any spark at all to fire up ecm.
 
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