Auxiliary battery keeps dying

I've got a 2004 Prius with about 90,000 miles on it, which I bought used about a year ago (so I don't know its whole maintenance history). Since the middle of May, the auxiliary battery has died 4 times after the car was not run for 2 days or so.

1. The first time, I called my auto club and got it jumped, and drove it to a major, reliable Toyota dealer. They couldn't find anything wrong with the auxiliary battery.
2. A few days later it died again, so I got it jumped and drove it in again. This time they said the auxiliary battery did seem to have failed. It was the original equipment, and due to be replaced anyway, which they did for $200.
3. A few weeks later, another dead battery after not running the car for a couple of days, another jump, another trip to the dealer. They told me a complex story that probably makes sense: there was carbon build-up on the throttle body and other areas, which caused the computer to think not enough gas was reaching the car to run it, so the car refused to start and the computer showed a low fuel code. They cleaned out the carbon for another $200. But I'd just given the car a 90K servicing at another shop, which hadn't found any carbon build-up; and if that's the reason, why did it start with a jump? Hmmm. After thinking it over for a day or two, they said that the carbon build-up caused a slow-idling engine which kept the alternator from properly charging the auxiliary battery, allowing it to run down. Hmmm again, but I don't know enough to say they were wrong.
4. Yesterday it was dead again. I tried to jump it from my wife's car, but couldn't get it started. I'm probably going to have to have it towed to the dealer.

I suspect there is some electrical-system snafu that is draining the aux battery, since it always and only happens after the car hasn't been started for a couple of days. But I know very little about these cars (and not much about cars in general), so if anyone has any specific suggestions to put to the dealer, I'd love to hear it. Is this a known issue with the Gen II Prius? Thanks for any ideas!

 

Hi everyone,

For some reason the PriusChat site would not see me as logged in to post a reply to the thread earlier, hence the private messages you all received! It's working now, so let me post a summary for all to see.

Thanks for all the various suggestions, including the no-alternator information. I thought this explanation sounded fishy. Though it's possible that the terminology got mixed up in being passed from a technician to a service advisor (not well-informed about Priuses) to me, this does not inspire confidence.

I don't drive the car every day, but usually 3 or 4 days a week, mostly on short trips, so maybe 30-35 miles/week. It seems to take two days of non-driving for the auxiliary 12V battery to discharge.

I passed everyone's ideas on to the service advisor at the Toyota dealership, who seems to be a reasonable person. This morning he said that a "parasitic current draw" is a possibility, which is what I've thought all along, so hopefully they will test for that, find one, and find out where it is. If not, I've got feelers out for other reliable shops in the area.

AFAIK, the only unusual electronics on the car are factory-installed Bluetooth, navigation system ... and a garage door opener built into the rear-view mirror. And when I thought of that (thanks, qbee42, for pointing me that direction), I remembered this: Recently I've noticed that the garage door opener is on every time I start the car. (I don't have a garage door, but the opener was on the car when I bought it used last year.) It didn't used to do this, but it's doing it now, and I haven't found a way to make it stop. I usually turn it off, but it's on again when I start up next time.

So: Is it possible that somehow something is turning this thing on when I turn the car off? Or, more likely, do I just not notice that it's on when I return from my errands and park the car? Would having it on be enough of a power drain to discharge the battery over two days or so?

A friend of mine says that he had a similar experience with a new Honda Element -- if the car sat 2 days the battery was dead. It turned out that an interior lamp had been staying on when the hatch was closed, and -- even after the lamp was switched off by the original dealer! -- there was enough current drawn over a couple days to discharge the battery.

So, I'm mildly optimistic that the rogue door opener could be the culprit. If so, I'm just going to have them disconnect the darn thing, since I never use it anyway.

 

You're right on target about the autodim, Patrick, which I didn't even know the car had. The service advisor at the dealership informed me this morning that what I thought was the garage door opener being on unnecessarily was in fact the autodim indicator, which isn't likely to be the problem, since it only comes on when the car does.

The thing about usage is, this only started happening in May, and my use of the car has not changed one bit. I drove it for a year in this way with no problem. In fact, if memory serves, we've been out of town for as long as 10 days a couple of times, and the car has started when I got home.

But now here's something else. Sometime last summer or fall, the audio on the stereo system went out. Other audio features (such as guidance system) worked, but not the stereo. I took it to a car stereo shop, and the guy disconnected the 12v battery and reconnected it. It seems that these computerized stereos sometimes get messed up and need to be rebooted, which is done by disconnecting current from the aux battery.

My recollection is that this happened after the car hadn't been used for a bit. And when we returned from a long trip out of town in early February, the stereo was again malfunctioning in the same way. I did without it for awhile, knowing the fix and just putting off doing it. When the dealership replaced the battery, the stereo started working again, and has worked ever since.

It's hard to believe that there's any connection between the stereo issue and the battery draining, but it seems to be very hard to figure out what's draining the battery in any case. I think I'll mention this to the dealership too.

 

Not only has the original battery gone dead, but so has the new one they put in in May. They're testing it now with yet another new battery.

Tell me more about the Optima Yellow top and fit kit. I'm not familiar with it. Thanks!

 

Thanks, Jeff, and to others who've replied. I've already paid $200 for a new battery, and at this point can't see shelling out nearly that much again, plus the work of installing it (or paying someone else to do it), even if it's better than the Toyota battery.

Meanwhile, something else has developed. I mentioned problems with the stereo system. They checked and found a TSB (Toyota Service Bulletin, right?) which states that the JBL amplifier may be staying ON when the ignition is turned OFF, which of course could result in a dead battery. An updated JBL amplifier is available to address this situation.

However, the car is out of warranty and the amp costs $1028.76 plus $100 labor to install. Don't think we'll be doing that.

So, any suggestions on alternatives? Driving the car every day (seems to defeat the purpose of owing a hybrid!), and getting a battery charger to use if I don't drive it every day, have already been suggested. I can live without the stereo, if they can disconnect it and fix the problem. Or can anyone recommend a cheap but reliable stereo for a Prius?

 

Thanks, Ed, and thanks to Patrick too for the salvage-yard suggestion. Obviously stereo-repair is not what a dealership specializes in, and I know a stereo shop I could take it to to see if the amp could be fixed. Meanwhile, I'm still waiting for the dealership to be 100% certain that it is the amp and not something else.

 

Well, the saga continues. The dealership did simply disconnect the power supply to the JBL amplifier, with interesting results: the stereo system has no sound, of course; but it also silenced the beeps when you press a button on the steering wheel or next to the screen. However, the GPS audio directions still work, as, of course, does the accursed reverse-gear beep. (But, thanks to Charles Suitt on another thread [Post #3] -- I silenced that myself.)

The dealership charged me nothing for doing the tests and disconnecting the amp, for which I give them credit (World Toyota in Atlanta). They admit it was a challenge.

So now, assuming that this actually fixes the problem (which I won't know for sure till I leave the car sit for a couple of days), what to do about the stereo? Several options suggested by an experienced local car-audio shop:

1. Call the Toyota regional rep and try to argue him/her down from $1000 for a new amp to something more reasonable. Sounds like a long shot.
2. Buy an amp on e-Bay or someplace, and have it installed.
3. Install a toggle switch or a relay to control power to the existing amp. I could switch the toggle manually when I turn the car off and on; or (he says) a relay might be hooked up to do this automatically.

I'd be interested in anyone's thoughts about #2 or #3. For #2: any ideas about good aftermarket sources? For #3: I like this one (since it sounds cheap!), but does it seem reasonable, given the electronics of the Prius, or am I asking for trouble having a stereo guy monkey around with it?

Thanks as always!