Toyota camry hybrid aux battery problems

We have a 2007 Camry Hybrid with an infuriating habit. It has a little auxiliary battery in the trunk which runs down if the car is not driven for a week, or sometimes less than that. This battery isn’t needed to crank the engine as in the usual straight-IC car, but it is needed to power the control computer, so without that, the car’s dead. We have taken it back to the dealer who seems unable to find anything wrong, and professes to be unaware of others with a problem like this. This time, ours died after two days in our driveway, so I started searching the web, and found this is not uncommon. There are reports of the problem striking people on the freeway, causing their hybrids to simply stop working in a dangerous situation. It seems that there is a constant drain on that battery to keep functions like the remote key and the security system and god-knows-what-else alive, But that applies to a lot of cars. Is this one a glitch-ridden lemon, or did the era of the vaunted Toyota reliability end a few years ago? How do I get reliable information on the frequency of this problem occurring? (It strikes Priuses and Highlander Hybrids, too.) How do I complain to the NHTSA and get a response? Any suggestions, other than putting big signs in the windows asking for other Toyota victims (er, I mean “owners”) with the problem to contact me? And is this a problem peculiar to Toyota, or does it happen to other brands’ hybrids, too?

Incidentally, one Prius owner says he was told there is some fine print somewhere specifying a minimum usage that the car has to get every couple of weeks, or the guarantee is voided, which seems a pretty bizarre notion. The dealer has never said anything to us about this.

Help! We are getting too old for this!

You could install a larger battery that has more capacity as one way to fix it. If you park the car outside you should be able to have a solar cell installed and it will keep the charge up. If you park inside then you may need to add a small trickle charger to keep the battry up while parked for a long time period.

been there. we actually did put on a solar charger that should have added between .5 and 1 Ah per day, and that did not solve the problem. The plug-in trickle charger doesn’t work at the airport. The larger battery, if it would fit, would just delay the inevitable. I’m wondering if this is a demon-possessed lemon, or if this is a common experience with other Toyota hybrid owners.

Incidentally, as I mentioned, it will run down in a week, hardly a long time.


You’re welcome.

The specs you gave for the solar panel sound a bit low to do what you want to do. It would be good to know what the current demand is on the battery so the proper size solar panel could be selected. I would guess that you would want something on the order of a couple of watts. That would handle about 200 milliamps of current. Most cars today I think draw between 25 to 35 milliamps of current to keep things alive while the car is parked. Any car will fail after enough time has gone by. A week is a bit short though without a doubt. You may want to consider adding another larger battery to extend the time period. Adding a battery like an Optima would make a big difference in the time period and safe to install in that area.

See if you can find out what the current draw is on your battery while the car is off. See if that meets spec with the factory specs. If you find out what it is let us know what it is. It would be good to know. Perhaps there is something causing excessive draw on the battery. So finding out where things stand is a good first start. The battery capacity may be low also.

If there is “some fine print somewhere specifying a minimum usage” you should be able to find it in the owner’s documentation that came with the car. I wouldn’t count on the dealer to tell you about it. Hard to believe the car warranty would be void, but the battery warranty might be.

Have you found any such requirement?

This "auxiliary battery’ must be a very small battery, probably to save weight. I can leave my non-hybrid car (with security system, radio presets, and all computers drawing the current they need for memory) sit for weeks at a time and the battery doesn’t go dead. This happens on a regular basis, not just once in a while. It takes about 6-8 weeks before I have to worry about the battery, and if I know the car will sit that long I hook up my Battery Tender Jr.

It’s also hard to believe these batteries are dying while the vehicle is being driven, unless the batteries are shot and the owners haven’t replaced them.

I’d consider installing a standard car battery in place of whatever this “auxiliary battery” is and see if it makes a difference. “Delaying the inevitable” can mean many things. If you can delay the inevitable for a month or two you will no longer have this problem.

And, yes, the era of vaunted Toyota reliability ended a few years ago. They’re still good, but not as good as they once were.

But, isn’t that true of us all?

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That solar panel estimate was a little complicated. Their nominal output is good, but they are losing because of the rear window being over them, plus not being at right angles to the sun, and I did one measurement and took a shot at what the changing sun angle was doing. So I could have been totally wrong. But I figured it would give me enough time to get through the week, even if it wouldn’t keep it full-up. it didn’t.

it’s at the dealer now, and i left a whole sheet of questions about that system. here’s hoping the electronics guy comes through. I told the service manager I thought about pulling certain fuses, and seeing how the draw changed, but he really did not like that idea.

I’ll let you know.

Any decent auto-electrical shop should be able to do a parasitic load test on the aux battery and isolate the problem…The circuits connected to that battery will be fused just like any other car…At least measure the drain (load) on the battery so you know what you are dealing with…If it’s a standard automotive 12 volt battery, you can only “deep cycle” those so many times before they lose much of their capacity…

That “auxiliary” is a bit of a misnomer. this is the one that runs the computer. there are stories of them dying on the freeway, so ppl just instantly find themselves coasting. It is small, probably because it doesn’t have to crank the engine. I left a sheetful of questions, including what the battery specs are, because the manual doesn’t give much detail at all.

I searched as well as possible, and couldn’t find anything about “minimum usage”.

i’ll let everyone know what I learn.

thanks, again

I’m about to start learning things myself if they don’t come up with more answers this time. I was a career engineer at NASA, and it’s really only the dreaded “voided warranty” threat that bothers me.
They replaced one battery already, and they seem to be lasting a year and a half. Pretty bad.
i do have some meters that could do some pinning down. I am not sure I trust the Service Mgr entirely because had a long thread that included engines that quit flat in the middle of the freeway, and he denied hearing anything about that happening. Hey, at NASA, if we heard of something potentially catastrophic, we generally got really curious. true or false, we kinda wanted to know.

I can understand you wanting to know about any failures on things at NASA. When things fail on those systems you can’t just pull over to the side of the road and see what happened.

The things you mentioned about the solar panel that reduce the efficiency need to be considered alright. That is why I think something that can handle a couple of watts may be suitable but I’m not real sure on that. When there is good light then there will be a good output to make up for the low output periods.

I don’t know how big the battery is for this or the capacity of it but perhaps something the size of a motorcycle battery or snow machine will have enough capacity.