Classic Prius Replacement 12-Volt Battery - Toyota Prius Forum : Prius Online Toyota Forums
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#1 (permalink) Old 03-31-2007, 10:19 PM
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Default Classic Prius Replacement 12-Volt Battery

I think my 12-volt battery died today. Has anyone installed the Westco battery offered by eLearnAid.com? Also, has anyone used an Optima battery?

I would appreciate any input before I proceed, as this doesn't look like a simple replacement like most cars. It's hard to believe that a routine maintenance item like a 12-volt battery should be so difficult. Why the heck didn't Toyota use a standard auto battery?!
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#2 (permalink) Old 04-01-2007, 12:02 PM
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Toyota didn't use a standard auto battery because the 12V battery isn't used for "engine starting applications". They needed a low current delivery "standby battery". A yellow top Optima would work very well - there is a size 51 available. Relatively small.

I suppose Toyota could have used a battery size like Honda uses in the Civic, but perhaps it wasn't available in a gel type or Absorptive glass matt (AGM) type (either is needed due to the interior placement of the battery). Be aware, even if you or I can buy one, it doesn't mean they are available in the high volumes needed for car production (at reasonable cost).

As for the rest of your questions, sorry, I can't help. If it was me, I would "adapt" the battery mounting apparatus and terminals and use the Optima size 51 yellow top. The Optima batteries are wound AGM type. The red top ones are for "engine starting applications" and the yellow top ones are for "standby applications/deep discharge".

Vehicle:
Pearl is a 2007 Driftwood Pearl Prius
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#3 (permalink) Old 04-01-2007, 12:26 PM
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Here's a link concerning replacing the 12v battery in a Classic Prius. Don't forget the battery needs to be vented.

http://www.mindspring.com/~dparrish/Pri ... Mods2.html
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#4 (permalink) Old 04-01-2007, 12:50 PM
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The MK battery part 12V31M is available from

http://www.elearnaid.com/12vobaforpr2.html

as well as a terminal adapter kit. As instructions to see your battery voltage on the little Prius screen.

Google 'mk battery 12V31M' to see other suppliers. See

http://www.mkbattery.com/

for their wharehouse locations.

DAS
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#5 (permalink) Old 04-01-2007, 01:20 PM
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Default Classic Prius Replacement 12-Volt Battery

Thanks for the quick responses.

I am actually interested in hearing about the experiences that people had replacing the 12-volt battery.

The battery and kit from eLearningAid.com looks like a good substitution, but has anyone actually installed the Westco Battery and kit from eLearningAid? The testimonials all sound kind of like they were written by the same person (the owner of the company?).

As for the Optima, I have installed those in other vehicles, including RVs; and I really wish they had a replacement that would fit this application. However, with the limited selection they offer, none have vent tubes, which is a concern with the battery located in the trunk. If the battery was under the hood or otherwise vented with outside air, this wouldn't be a problem. However, the possibility of hydrogen gas buildup in an enclosed compartment doesn't sound like a good idea.

I suspect that the 12-volt battery in the Prius is kind of like a battery in a computer UPS (uninteruptible power supply) or on a trickle charger, and the likelyhood of the pressure valves opening on the Optima are remote. However, if this somehow did happen, all of the acid and gas in the trunk could be disastrous. And, I don't mean just ruined golf clubs and clothes. I am thinking more about explosion and fire.

Therefore, I am interested in how people have circumvented the Toyota replacement with an aftermarket solution. Are there any happy campers out there with Westco or Optima batteries?

===============

By the way, we limped home about 20 miles after I got the error screen. Unfortunately, this was our second attempt on Saturday to go to the Arizona Sonora Desert Museum in Tucson with our grandkids.

The first botched start was with our 78 Chevy Pickup & travel trailer. We only made it about 1/2 mile from home; just far enough to have to be towed back. After moving some of the stuff to the Prius and making hotel reservations in Tucson, we started off again in the car. I should have realized that the stars weren't with us yesterday, when we got detoured off of I-17 into south Phoenix, down by the airport, due to construction. The dreaded triangle of death occurred on the off-ramp.

What a start to the weekend -- Four hours after we first left on our road trip, we have two disable vehicles in our driveway.

I hope everyone had a better weekend than we did!
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#6 (permalink) Old 04-02-2007, 11:00 AM
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That doesn't sound like a 12V battery problem. Once you are in READY, the 12V battery isn't really in the picture. Rather, the DC-DC converter in the inverter assembly converts the 200+V down to about 13-14V for the 12V electrical of the car. Unless the 12V battery develops a dead short in one of its cells thus loading down the 12V power feed to the whole car, it wouldn't be causing problems once the car is in READY.
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#7 (permalink) Old 04-02-2007, 03:57 PM
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Default Classic Prius Replacement 12-Volt Battery

I guess I'll know for sure in a day or two. I ordered the Westco battery from eLearningAid.com, and it should be here later in the week.
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#8 (permalink) Old 04-03-2007, 12:50 PM
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Default DIY battery tales

On 2001 Prius, my first 12 v replacement was the MK 12V31M which I picked up in Anaheim CA. I hacksawed the lead terminals down to the correct size, as a brutal alternative to new connectors. I think Dave Dorrance put some of my pictures etc. into his website.

Unfortunately that battery lasted only a year, and the negative terminal especially became very corroded. I suspected that my cutting was not such a good idea.

Then I bought an MK U1 battery, similar but unvented and with flat drilled tab connectors. Price was a more comfortable $25, at a pawn shop(!)

Unvented is unapproved in Prius, but there are a few who feel that risk is overstated. With only slight modification the bolts in the Prius original connectors did fit. This one still shows a very high resting voltage after another year and no corrosion. Think it's going to be a keeper.

DAS
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#9 (permalink) Old 04-03-2007, 01:25 PM
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I was thinking about such a battery. We went fishing on a boat and they had a 34AH battery running a pump for the bait fish tank.

I asked how much they paid for that battery, they said $40 for 2.
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#10 (permalink) Old 04-06-2007, 03:15 AM
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Default Classic Prius Replacement 12-Volt Battery

Received the battery yesterday, but vent tubing arrived separately, today.

The Prius adapter kit contained a negative ground cable, a positive terminal that accepts the fuse block, and vent tubing. The parts look like they would cost about $6-8 at WalMart, if they were commonly available. However, the extra money was worth it to me to avoid the quest for off-the-shelf parts that would require customizing.

The installation was simple and only took about 15 minutes.

While not especially a great bargain, the battery is as advertised, the price is fair and all the parts fit. This sure beats the Toyota dealer. If I had let them work on the car last Saturday, I would have been down $92.50 for diagnostics BEFORE I ended up paying a couple of hundred dollars for the battery.

While all screens returned to normal the first time I started the car with the new battery, the check engine light was on, initially. However, after letting the ICE run a minute or two and shutting down, the check engine light was gone when the car was restarted. I hadn't realized before, but the headlights and dome light had been really dim for several weeks and now they were bright again.

In summary, I ordered the battery and kit on Monday, and they were shipped free via UPS Ground the same day. The battery arrived on Wednesday, and the vent tubing arrived today (Thursday) via USPS. (A phone call on Tuesday said that the tubing was accidently omitted and was being mailed separately.)

As far as I am concerned, this is about the only viable option to the Toyota dealer, and I didn't have to leave my car there over the weekend. Also, I saved enough money to cover my fuel expenses for the next four months. So, I guess this was a bargain.

By the way, after I got the old battery out, it had a shorted cell and was only putting out 10.5 volts. So, the computer was running under brown-out conditions. I'm really glad this wasn't more serious, and that it happened so close to home. Considering I had to order the battery over the Internet, it is unlikely we would have found a replacement so quickly in Blythe or 29 Palms on our frequent trips to San Francisco. If I had noticed early symptoms a month or so ago, we could have replaced the battery before ruining this past weekend.
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