replace 12V battery or get a jump?

I haven’t had any trouble with my 2007 Prius until last night. I was at the gas station, trying to close the window after talking to the attendant (no self-serve in OR). Just as it was dawning on me that the window was closing very slowly, the MFD beeped and gave a message about a transmission problem, “park on a flat surface and fully engage the parking brake.†Then the MFD went black, though the radio kept playing.

The car was turned off, of course, since I was getting filled up. Managed to start up and drive home (2 blocks), and when I went out to investigate later in the evening, the cabin light and MFD were very dim. I haven’t measured battery voltage but imagine it’s pretty low.

My question is, do I need to replace the 12V battery at this time, or would a AAA jump suffice for now? Four years and 61K miles doesn’t seem like a long enough lifespan for the battery. The gas station was the second stop on the way home yesterday – 15 miles of highway commute then one brief stop, then another couple miles to the station. No problem starting the car until I tried to start her up last night to swap cars on the driveway to have a known-working ride to work today. I don’t think I left any lights on or doors open, and even if I had – wouldn’t that have caused problems when I tried to leave work yesterday? No way I could have drained it during that 3-minute stop.

This car is a daily driver, c30 miles round-trip commute and odd jogs on the weekends. Weather’s been around freezing and dry lately, so I’ve been driving with the defroster/heater on quite a bit, but never try to run those without having the car in Ready mode. I can’t think what I might have done to drain the battery, and I’m surprised it’s dead. Also, I haven’t been seeing the odd symptoms reported by other PC posters, fluctuating SOC readings and the other odd things that happen when the 12V battery starts to go out. So, please advise – jump or replace?

If the battery is the original, it's near the end of its useful life - replace it.

I would replace the battery for your own piece of mind. From the sounds of things you have never had any issues with your car and now you feel as though you can't trust it, change the battery and regain your trust in the car that has served you so well for 4 years and 61K miles

Batteries are expendables. 4 years is about when I change batteries, regardless of condition. And a jumpstart will not rejuvinate your battery. It will get you going, allow the car to partially condition the battery, the more you drive. A decent, low amperage intelligent charger hooked up for one-or-two nights will do better, might even wring another year's use out of it. But it sounds like your battery's days are numbered.

A jump never fixes this. You might be able to save it by putting it on a trickle charger for several hours, at 3 amps or less. But usually, when it get to the point that you describe, you are better off to replace it.

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My 12v battery is nearing the end on my '07 with 39k miles. That's a pretty good life for the stock battery from what I've read--some only last 3-4 years. I get the red triangle when I start the car if I haven't had the smart charger on.

I plug in a 1-amp charger to the 12v system about every week overnight so I haven't had any serious problems yet. I don't know how much longer I'll get away with it though.

I agree that a jump start won't get you very far. The 12v charging system on the car is low-current so it doesn't charge the battery very fast or very well.

Also, be very careful jump starting. A reverse-polarity connection does extensive damage to the Pri electrical system--triple check the polarity.

Although Optima does now have the direct replacement application for $199, I'm going to go with the Group 51 Optima with adaptation kit from Toyota Prius 12 Volt Auxiliary Battery with install kit for 2004 - 11 for $170 (includes shipping). A bit of cost savings plus the ability to use a more commonly-available group 51 battery. The Optima yellow tops should last much longer than the Toyota replacement.

Eric

Does anyone have an idea what a factory type 12 volt battery cost is from a Toyota dealership? I've looked at the usual parts stores and struck out. Seems to be very unique to the car.

I've got 190,000 miles on my 2007 and still on the original battery and feel it is on borrowed time and with my wife now driving it, I don't want her to have any trouble. I just got a used 2010 with 7,000 miles on it so I hope to be trouble free for a long time.

Hi tidan1....I had a battery installed yesterday at one of the dealerships in Milwaukee and cost was $201 ($226 - $25.00 for a service coupon they sent me)..and they washed the car + gave me a free bag of cookies. It took them less than an hour.

These batteries are unique and this site has very good information on how to check the battery voltage and how to install one if you choose the Optima battery route.

My suggestion would be to check for a service coupon (these are on-line too at dealership) and call the them and ask what it would cost and then decide.

Good luck

This should be a sticky

The original battery, a lead acid type doesn't have enough strength to last 1/2 hour running the radio in acc mode, it's inadequate. If it goes dead once, it's toast, it's designed to start the car in warm weather and it's good enough to get a new car off the lot of the dealership.
When replacing use an Optima Yellow top, which is a deep cell (can be drained and fully recharged repeatedly) gel(no lead acid gas) OEM (original equipment manufacturer) battery, it's a direct fit for the original and will result in better mileage because the ICE is running less, it doesn't have to keep charging a dead or dying battery.
Buying another battery from the dealer is simply putting in another lead acid battery inadequate for the job it's being asked to do.

The OEM Battery is a AGM battery and NOT a lead acid battery. IF: you are a DIY'er you can put almost any battery you want in the car and save a lot of money. If, you are not a DIY just go to the dealer and pay your money.

Just did this to my '07 w/ 115k. As Patrick said, take it out, peel off the label, take out the clear strip covering the caps and then pop off each little rubber cap. Unfortunatley on mine, the battery is Not clear but a black case, ie. can't see through it to get an accurate level indication. On mine, three of the six cells were below the top of the inner plates as far as fluid level. Added distilled water to bring all 6 cells up, reassemble and back in business. Was done about a month ago, no issues.

Just be careful not to lose the little rubber caps and pay attention to fluid level if you don't have the exterior markers on the case. Do Not fill up to the top w/ water.

Oh ya, cost = 0 (Already had the distilled water).

Well, gleamed the above from:
http://priuschat.com/forums/gen-ii-...-battery-needing-replacement.html#post1425234

So one persons AGM is another persons lead acid battery.

AGM = sealed lead acid, rather than flooded lead acid. Having flooded lead acid inside the passenger cabin is considered unsafe.

I did the same, just used filtered rain water from last year, (aged)

I forgot one important warning, only fill cells to top of cells, not to top of opening, then charge, then after charge, pour in some more water, if you like. The reason for this is: If you fill to top or close to top, the electrolyte expands and can overflow while charging.

I can highly recommend the Optima AGM batteries. I replaced mine with the eLearnAid kit in December 2008 after an aftermarket accessory issue drained the battery flat 2x in 2 weeks. What I can confirm is that after flattening the stock battery, it is a road-side assistance call waiting to happen. I'd also recommend dragging a booster jump pack with you until you can get the battery replaced and do yourself the favor of putting it in the back seat, NOT the hatchback accessory tray. When the battery goes flat, getting it out of there is a hassle. (Voice of experience there.)

I liked the Optima AGM product so much I bought a deep-cycle AGM for my camper and went from replacing the battery every other year because I was down to under 1/2 battery performance after the end of the 2nd season to being 3 seasons in and still getting 90% run after the end of season 3. If you're keeping track, I abuse the heck out of my deep-cycles. AGMs are also highly resistant to shock, so you'll never get a dead-short cell if you bounce around 4-wheeling.

I keep a small sealed alarm battery, in an old fannypack under the rightseat and charge fromm time to time when driving, from accesory plug.

I was thinking about using a RV Battery Isolator/Combiner setup so you can have an always-maintained backup battery. You could also accomplish this a smart 12v to 12v charger wired to a switched circuit and a switch to connect the battery to a non-switched circuit.

Filtered rain water? Ew. You were kidding, I hope.

Must be for the acid rain.



Rainwater is not deionized. Even distilled water is better than rainwater, since rain falls through a lot of air, picking up bits and pieces along the way.

Tom