Replacement of 12 volt auxiliary battery

Where can one obtain a replacement for the 12 volt auxiliary battery in the Prius? What are the specifications (e.g., product name, capacities, etc) and prices of the replacement 12 volt auxiliary battery?

Toyota dealer mostly. There have been some that made retrofits of other types.

1. Needs to be sealed. There should be no way to spill any elecrolyte.

2. Needs to be vented if there are chances of dangerous gasses that will, or can be released.

3. Needs to be 12V. 13.8V to be exact. The DC-DC converter determines if it goes into charge mode (14V) based on sense voltage.

4. Needs to have 28AH capacity. Can be greater if space allows.

5. Needs to be able to tolerate large charge currents, at least for a short term. The OEM battery is said to take a 3A charge current, though it baffles me that the DC-DC converter outputs 80-100A with no current regulation to the OEM battery, other than the fuseable links' inherent resistances.

6. Needs to be able to provide 100-150A. Granted, it won't provide this for long with a 28AH battery.

6. Needs to fit or be retrofitted to the provided storage space in the underhatch.

7. Needs to have the right posts, or the wires altered to accomodate the new posts.

Found what appears to be replacement for Prius 12 volt auxiliary battery. Check out at www.westcobattery.com/_page.php?bid=20&vid=-1. Does this battery and its characteristics make it suitable as replacement for the Prius 12 volt auxiliary battery?

Westco Battery 12v13m Sealed AGM Battery. CCA 475 Length 7.5" Height 7.25" Width 5"
Weight 25 lbs. MSRP 89.95 includes shipping

You mean 12V31M, http://www.westcobattery.com/miata.html ?
I believe someone did a writeup on retrofitting such a battery. Post terminal clamps had to be replaced.

CCA not relevant here, you can't draw more than 150A without blowing the fuseable link, and you aren't cranking anything with the aux battery.

Update for replacing 12V Auxiliary Battery

I've had to replace my Classic Prius 12V battery and now my 2004 Prius 12V battery, here's some ideas:

For the classic, model year 2001-2003, try this solution:
http://www.elearnaid.com/12vobaforpr2.html
This is a 12V31M Westco Sealed battery for US$108.95, you'll also need a kit which includes parts needed to adapt to standard terminal size here:
http://www.elearnaid.com/pakitforup12.html for US$25.00

I had purchased the 12V31M Westco elsewhere and went to a few auto stores getting post adapters, a new negative cable, vent tubing, and fashioning wood blocks for making the hold down work, and would have rather have had a kit like the above had I known about it.

For the 2004-2008(so far) Prius, try this:
http://www.elearnaid.com/12vo1topraub.html
D51-YT Optima Yellow Top Sale price: US$140.00, you'll also need a kit which includes parts needed to adapt the standard terminal size here:
http://www.elearnaid.com/pakitforinop.html for US$10.00

I went with a replacement at my local Toyota dealer(today) that they had in stock and replaced the existing battery myself after 4 winters on my 2004 model with Smart Key and Navigtion(purchased 12/1/03):

Toyota part number: 28800-21170 (also marked S46B24R on the battery itself and on the outside of the box Toyota sells you the battery in), I paid $138.70(apparently list price), better price here:
http://www.toyotapartscheap.com/
just search by factory part number 2880021170 to find it for US$110.96
No kit needed, it's an exact match to the battery being removed.

An amount of effort was needed to unscrew the 9 bolts & screws(using 10mm and 12mm socket wrenches) to move the large plastic vent out of the way, move the brake assist out of the way, remove the battery bracket, detach the vent tube, and move the positive and negative cables out of the way to remove the old battery. When placing back in, I would recommend this order:
1. Install new battery with battery bracket(1 bolt, 1 screw)
2. Re-install large plastic vent(1 bolt, 1 bolt/screw) Take care not to lose that bolt/screw and really reach for it.
3. Re-attach the vent tube.
4. Re-install the brake assist unit(2 bolts to floor, 1 on top of assist unit)
5. Re-attach positive post.
6. Re-attach negative post(Please leave this for last, because, as you'll see, there is only one way to tighten with the 10mm socket wrench. Gently turn the negative connector so that the socket wrench can be placed back in, and so that others can get to it later on. This will also allow you to remove the negative connector in the future without taking the rest of this jumble apart)

And although I left all my positive connections connected to each other before and after removing the connector from the postive terminal, I would still highly recommend this great description with pictures for taking the above listed items apart(for either/any battery replacement 2004 or above):
http://www.techno-fandom.org/~hobbit/cars/prius-12V/

Good luck and have fun!!

-John T

P.S. I had tried the Sears route, but the technician took one look at the vent tube and said he could not install their recommended battery for the Prius because it would vent into the passenger compartment. He also said he would get the entry removed from the Sears database for Prius for safety reasons. My opinion is to stick with these(or other batteries) that can be vented via a tube outside as in the original design of both the Classic and current Prius.

Anybody know enough about battery technology to say whether the one from eLearnAid above is actually a better battery, and worth it ?

Hope there wasn't any confusion in my previous post, eLearnAid doesn't make batteries, but is only a reseller.

The 3 batteries mentioned are:

Westco 12V31M (for 2001-2003 Prius if post connectors are adapted to standard size)
Optima Yellow Top D51-YT (for 2004+ Prius if post connetors are adapted to standard size)
Toyota 28800-21170 (S46B24R - matches original on 2004+ Prius with smart Key and Navigation, does not need to be adapted)

For me, my goal was to get a replacement battey that would be as good or better than Toyota's AND would be properly vented to the outside. I found WestCo's from other forums and previous posts here and have been very satisfied with 3 years of use(on my 2002), so far. I am also satisfied with the original battery from Toyota(on my 2004) and replaced it with the same, but with price quotes from $110 -$199 battery only and $175-$300 installed, I was looking for "other" solutions to consider.

IF I were to adapt the connectors to fit a standard post battery like WestCo's again(or the Optima I was considering), I would purchase the $10-$25 kit from eLearnAid, instead of finding and/or making the parts myself, simply from a time savings perspective. (However, I am using their quick disconnect switch on my 2002 for multi-day cold weather parking, nothing too special, was just tired of jump starting in the cold when parking at the airport for a week)

Since, I did not find a replacement battery solution like this for my 2004 elsewhere on this forum, I thought I would post my findings for anyone else interested in adapting 3rd party batteries more easily, or simply some links, and some info to help replace their existing 12V on their own. (Special thanks to Techno-Fandom's "hobbit" for their post which encouraged me to take apart the "jumble" in my 2004 and replace my own 12V battery)

Making a more standard, and yes, much less expensive battery fit and work for starting, but have the potential to gas into the passenger compartment was not satisfactory to me or my family.

Can you describe for me the symptoms that lead you to conclude you needed a new battery in your 2204 Prius? I'd just like to have that reference point when my 2007 needs one someday.

Thanks

please see my post in the technical forum

http://priuschat.com/forums/showpost.php?p=525166&postcount=17

The Optima battery is a better quality battery than the stock one available from Toyota. The question is, does it matter? Lets look at the features and benefits of same:
1. Optima will withstand much greater vibration - this wouldn't give any benefit in a Prius. Perhaps in an off-road application.
2. Optima is a "AGM" battery. The electrolyte is held in a glass mat, so in the event of an accident (collapsing the right rear fender), if the battery case is broken there would be no spilled electrolyte. I have seen broken Optima and gell cell batteries, and it's true the electrolyte will not spill. The stock battery would leak sulphuric acid into the fender well, and elsewhere if the car rolled.
3. The Optima offered is a higher capacity compared to the stock battery. This could be of benefit if you frequently subject the battery to serious discharge. The larger capacity would lengthen the life of the battery, as you wouldn't get as close to full discharge with it.
4. The Optima yellow top is a "deep discharge" battery designed for "float" applications, exactly what the Prius needs. I don't know if the stock battery is a deep discharge unit. It's important to remember that even though a battery may be designed for "deep discharge" use, it will suffer damage if fully discharged. It just suffers less than a "normal" lead acid battery. So discharge carefully!
5. Be aware the Prius maintains 13.8VDC on the 12V system when "on". Unfortunately, it doesn't seem to compensate for temperature (the voltage should go up as it gets colder, and down when it's hot - about 14 V at 0C and below, 13.6 V at 30C and above, or there about).
6. The Optima battery is heavier than the stock battery. Probably around 10 lb difference (I haven't weighed them). This will make the car heavier, which would in theory decrease mileage. I doubt anyone could measure the difference with such a small weight change.
7. The Optima battery looks cool! This is the most important feature!

Experience with the following Prius' in a Chicago winter, my 2002 Silver(sold), my 2002 Blue Moon, and my mom's 2001 Silver, plus this 2004 now have had the following symptoms just before needing(or wanting) to replace the 12V battery:

1) A "dimming" of the gas guage and 0 on the speedometer, as the car is being started, just before the "Ready" light comes on. Near the end of the battery life, the display is barely readable, and then suddenly brightens up each time as "Ready" comes on. Before "Ready", the display is soley powered by the 12V stand-alone, after "Ready" the 12V system is also being fed through a converter from the hybrid battery, which is also charging the 12V battery.

2) Needing to jump start the 12V system when no accessories were left on prior. (And perhaps doing this a few times, usually in colder weather, before realizing, it's time to replace the 12V)

3) Very dim, and noticible, dome lights, and/or hatch light when car is not in "Ready" mode.

4) More to my situation of "wanting" to change a battery: having a spouse and 2 boys(over the years from 0 to 6 now), who would leave dome lights on, trunk/hatch open, doors open, and even sitting in the Jewel(grocery store) parking lot with the radio on for 15 minutes at 0 degrees outside(in accessory mode, NOT in "Ready" mode) thereby draining the 12V battery and requiring a jump start several times over the lifetime of each battery.

This time on the 2004 I had the Point 1 symptom towards the end of last winter/spring and then for the last 3-4 weeks. Then, last week, a drop in temperature midday, from 48 degrees being stored in my garage, to 20 degrees while parked outside for 45 minutes, allowed me to get only one Smart Key unlock, then everything, security system, unlock/lock, just everything went out(no response, no lights anywhere). A quick jump(Point 2), plus knowing that winters here will still get colder over the next couple months, PLUS typical use of my 2004 for very short "kid trips" convinced me to replace now before getting stranded.

As to point 4, the original Classic(2002) battery went pretty fast, but the replacement Westco battery is holding up very well. Also our Westco battery on the Classic is currently getting charged well twice daily on a 45 minute commute.

BTW, bringing the original 2004 12V battery indoors, warming up for 6 hours, and then throwing on a 2 amp slow charger, brought it's voltage from 10 volts to just over 12 volts(and the slight battery buldge also went away). I sorta wish I had just done that and waited to see if I could get through another winter(watching for "dash dim" carefully), but instead I get the feel-good feeling of having a new 12V battery and peace of mind.

Also, if you haven't jump started a 2004 or newer Prius yet, take a good look at the order and where the cables get connected under the hood, and make sure to unsnap the access for the positive connection, it's pretty tight and a pain the first time to open(especially in cold weather or with poor lighting, and hey[safety disclaimer], use gloves and don't touch and other metal part of the car while touching or working with a positive[red] connection). Also test to make sure that your jumper cable clips aren't too large to make the connection there, before you need a jump.

John,

Thanks for the tips and the well-described "precursors" to battery failure.

I have found that it is much less costly to my personal well-being simply to replace a car battery after 3 years than to wait for it to complain -- whether the complaint be bang or whimper or " ".

Still, my business partner only now replaced the 12V on his 2002 Classic. Five years seems like a long time for one of those little batteries. Fun to say he had it so long, but not at the expense of being stuck outside in the December cold.

Funny you should mention that, our 2002 Classic's Westco battery just went dead after sitting outside last week in 0 degree(F) weather, while getting checked at the dealer for engine non-start error messages in cold weather only. Besides the "extended Platinum warranty" coverage of the $3,000 plus to replace engine CPU, steering CPU, and steering column(again?!), they wanted $284(from my pocket) to replace the 12V battery.

When I picked up the car, I jumped started, drove home and placed my second Westco battery into this vehicle. BTW, no error messages at all even after changing out the 12V battery completely. Much different behavior as I've been so used to getting triangle screen messages after any battery disconnect since original date of ownership in '02. Glad to see the engine CPU replacement gets rid of that problem.

Just to note, we're on our 3rd 12V battery due to the fact of my family leaving car doors open, dome lights on, usually outside overnight and/or for multiple days in 0-32 degree(F) weather, so I am VERY pleased with the previous performance of the Westco for 3 winters after having drained it for no less than 6 times during its use. Seriously, drained to where the door locks and security system had no power to them.

Oh good! Another battery thread revitalized for me to post my Optima installation in!

Prius Optima Aux

I just did the replacement today. Background:

New '07 Prius package 6 on 30 April 2007.

Foot surgery 20 Dec 07. Couldn't drive for 3 weeks. Prius parked in garage in So Cal (maybe it got down to 55 degrees).

Went to start it - dead. And, I mean *DEAD*. And, I'm sure that everything was properly powered down.

I charged the battery, got a float charger, kept it on there afterwards. Everything seemed to work OK.

On the Monday before super tuesday, I listened to the radio (accessory setting only) for about 20 min about the California propositions. That was enough to finish off the battery.

So, the ability of the battery to take a charge was shot (More importantly, I no longer trusted the battery to hold a much of a charge). I ordered the Optima kit (battery and conversion kit) yesterday morning. It arrived this noon. Put it in, no problems.

Given that the Prius is a computer-on-wheels (with a relatively high parasitic load) and doesn't have a conventional 12 Volt starter, it makes far more sense for it to have a deep-cycle battery instead of a high current but shallow cycle starting battery.

I was absolutely astounded by how soon I got the battery after ordering - about 26 hours. Way to go, elearnaid.com!

I hope that this will put my battery concerns to rest.

PS - Why didn't I use the warranty? Because I didn't want to hassle to get a new crappy battery for free. What's the point?

PPS - Can we put Darelldd's post on the Aux Battery Replacement with an Optima Battery as a sticky on the care, maintenance & troubleshooting forum?

I weighed the original battery from my 2006 Prius with Smartkey system. It was 28.88 pounds.

I don't (yet) have a sample of the Optima to weigh. The specs for the Optima D51R (note: I have since learned that the battery for my Prius should be D51 without the "R") on Optima's web site quote a "minimum weight" of 26 pounds. Amazon mentions 26 pounds and 28 pounds, another web site quotes its weight at 29 pounds.

So I conclude that the Optima will weigh "about the same" as the original battery in my car.

I've read that the Prii without the Smartkey system come with a smaller battery. Comparing my measurements of the physical dimensions of my battery to the measurements Hobbit posted it looks like his is about 20% less volume, so for constant density it would probably be 5-6 lbs lighter.

I know . . . too much thought and analysis for a minor detail. I keep forgetting that an extra few pounds in a Prius is not as big a deal as an extra few pounds on my bicycle. And an extra few pounds on the bicycle just means a better workout when I leave the Prius parked in the garage, which probably means an extra few pounds I'm not carrying around under my skin all the time. But leaving the Prius parked in the garage means the stock 12V battery lets me down when I finally want to drive somewhere . . . which is why I started reading this thread. And I'm babbling now . . . good bye!

Added 8/22/2008: I just acquired an Optima Yellowtop 51R (note: I have since learned that the battery for my Prius should be D51 without the "R") battery at Costco in Eugene OR for $139.99 with the promise of a $25 rebate. The weight of this one is 27.20 lbs.

I am REAL confused about one thing. On one thread I read that the 12V battery is NOT used to start the car, and on this thread folks write that once the 12V is low or dead that they can not start the car.

Folks, which is it??? Besides the many computers, lights and gadgets, what else, if anything, is this battery used for??

Thanks all for all of the good ideas and photos on how to replace this battery.

The 12V auxiliary battery is required to power up the various vehicle ECUs. Once the ECUs are on, then the system main relays (located within the traction battery case) turn on so that the traction battery can provide power to the inverter. MG1 receives power from the inverter and spins the ICE, to start it.

If you decide to buy an alternative to the correct 12V battery provided by Toyota, I strongly suggest that you verify the battery terminal polarity is correct, as you can cause substantial damage by incorrectly connecting that battery.

Should be D51 WITHOUT the R!

So I finally got around to installing the D51R Optima Yellotop I picked up at Costco
--D'oh! Doesn't fit right.

I had the idea fixed in my mind (from past messages I saw on PriusChat?)

that the battery which fit in a Prius was the 51R, but in fact it should be group 51 (without the R.)

I'm kicking myself for not double-checking this. Especially since I did take the old battery out and look at it, check it's size with a tape measure, weigh it (!?), and generally obsess about many aspects of the replacement--all before I bought the Optima and install kit. An additional bit of self-esteem bashing irony is contributed by the fact that my other car ('93 Honda Civic) actually

• does take a 51R
• was parked right by the Prius in the garage
• probably had the hood open and a battery charger hooked up

when I was doing my pre-purchase almost-due-diligence. I could have easily compared the battery from the Prius and seen the difference, if I'd only thought to double-check that aspect. :boink: At least Costco has pretty good return policies.

For anyone who's interested, the difference between a group XX battery and a group XXR battery is in the position of the terminals. They are mirror images of the other, kind of like a left and right hand, or like L-somebiochemical and D-somebiochemical. Things which have this chirality property can be identical to each other in every other way and yet still not fit and function in all of the same places (turns up in biochemistry quite a bit.)

The attached image illustrates this with the original battery from my Prius and the new 51R which doesn't fit. The human fingers in the picture are pointing to the positive terminals. The new battery could be installed two ways: 1)positive/negative terminals at the wrong end or 2)terminals on the wrong side. It probably could be made to work with longer batter cables or something . . .