Replacing the 12V Auxillary Battery

[ryanca]

The 12V Auxillary Battery in my '02 Prius has come to the end of its life and needs to be replaced. I removed it from the car and had it tested at AutoZone, who confirmed that it was dead. Interestingly, AutoZone said they could not replace the battery, because they had no record of it in their systems.

I called my local Toyota dealer and they said that the battery can be replaced with either Toyota part 28800-21050 or 28800-21190. However, both of these cost $138, which I feel is a little steep for a car battery. Is there something special about this battery, or is it OK to replace with a standard, 12V car battery, such as one that can be purchased at AutoZone?

I just don't want to damage the hybrid system if there is something different electronically about these batteries. Anybody have any thoughts or experience on this? Thanks!

[tochatihu]

There be no electrical difference. Prius 'issue' is a vent tube to expel rare, unwanted gases from the common area, inhabited by you as well as the thing.

Your $138 price from Toyota is lower than I have heard before. The standard suggestions have been elearnaid's battery and terminal kit (google it), or the same battery from MK with you making the terminals compatible.

If you choose to believe that venting is not a critical requirement, a world of non-vented, about-30-amp-hour, 12 volt batteries opens up to you. Those could cost as little as $30.

Fair warning, the issue of needing venting remains somewhat contentious! As I have said so much already, expect to hear some strong opinions on the subject.

Back to basics, if you use a battery much smaller than 30 Ah, it will not manage the key-off parasitic load for very long. If OTOH you choose one larger, it will certainly weigh more and your task is that it should fit in the space available.

Please never use any lead-acid battery in Prius without securing it well in place. Make its terminals free of corrosion, and keep them that way. That's about it.

[ryanca]

<div class='quotetop'>QUOTE(tochatihu @ May 12 2007, 03:57 PM) [snapback]440701[/snapback]</div>

Prius 'issue' is a vent tube to expel rare, unwanted gases from the common area, inhabited by you as well as the thing.

[/b]

tochatihu, thanks for the link to the Elernaid kit. One question, though, I disconnected the current battery already and didn't find any trace of "venting" installed. There was a large black vent hose running behind/above the battery, but it was not connected to the battery in any way. Also, it was not very securely sealed.

Recently, I was in a collison and the side of the car near that battery was repaired. Do you think the mechanic never replaced the battery vent hose? I'm really glad I checked here first, thanks!

[JimN]

tochatihu, isn't the 2002 Prius the sedan? If so, the battery vent is on the side of the car.

[efusco]

http://www.mindspring.com/~dparrish/Prius/...tteryMods2.html
http://www.elearnaid.com/12vobaforpr2.html
http://www.mkbattery.com/



<div class='quotetop'>QUOTE(JimN @ May 12 2007, 09:24 PM) [snapback]440797[/snapback]</div>

tochatihu, isn't the 2002 Prius the sedan? If so, the battery vent is on the side of the car. [/b]

That's the intake for cooling the HV battery you're thinking of.

[c4]

I replaced the stock Toyota battery with a Honda Civic battery- you need to order the version with the correct terminal orientation, but it's similar enough in size that you require minimal modifications to the bottom tray (it's got slightly greater width and about the same depth), and you have to fiddle a bit to get the top securing strap down (it's a tiny bit taller).. Then the battery terminals on the vehicle have to be replaced with North American sized parts.. The ground terminal is easy, just buy a pre-wired terminal and replace the OEM version; this is is IMO better than just replacing the terminal because the OEM ground wire is somewhat thin, and the replacements are typically much heavier gauge.. For the positive terminal, I got a "marine" terminal with the wingnut fastener on top- replace the wingnut and bolt with the original nut and bolt from the OEM positive terminal, and the new terminal basically bolts in place on the end of the original positive wire without any need to drill or hacksaw bits and pieces off..

Best thing is that the new battery is a true AGM battery with no free electrolyte (all in the mats) vs the OEM battery which the Toyota literature claims is AGM, but in reality is a regular wet cell with sloshing electrolyte inside..

I did *NOT* put any kind of vent tube in my car (a Classic Prius) because the new battery is AGM and has far lower gas emissions than the original liquid filled version and additionally, the hybrid battery cooling/vent system also happens to have a duct ending in the 12V battery well and this big duct by itself is much more effective in dissipating any hydrogen emissions than the tiny rubber hose which was probalby put on as a "just in case" measure..

[ryanca]

Hey everyone, one more question. I'm looking into the Elernaid kit ( http://www.elearnaid.com/12vobaforpr2.html ) but it says that the kit may not work well for Priuses that had the Panasonic auxillary battery installed. Apparently the mounting tray is different(?) Turns out that my Prius did have the Panasonic battery rather than the original GX, so would I be better getting another Panasonic from the dealer? Apparently I can get it for about $138. Or would it be better to try and make the Elernaid one work?

I would have never guessed that this 12V auxillary battery could be such a hassle!

[efusco]

Choice is yours. If it were me I'd just avoid the hassle, shell out the $138 and get the OEM battery and be done with it. It'll probably last the life of the car.

[c4]

<div class='quotetop'>QUOTE(efusco @ May 13 2007, 10:21 PM) [snapback]441376[/snapback]</div>

Choice is yours. If it were me I'd just avoid the hassle, shell out the $138 and get the OEM battery and be done with it. It'll probably last the life of the car.
[/b]

Actually, the fact that he's looking for a replacement means that the OEM battery has *NOT* lasted the life of the car.. 5 years is pretty average for the life of a lead-acid car battery.. I don't know about you, but I fully expect my Prius to last a lot longer than that..

I decided to go with a larger standard battery because #1, it's got a much higher capacity than the OEM and if I park it outside in an airport park-and-fly lot for 2 weeks in a Canadian winter, I'm absolutely *not* worried that I might come home to a dead car.. The fact that the battery was half the cost, even with the new terminals, and easily available from any auto-parts store was also a big plus.. Lastly, I've long beein of the opinion that the 12V charging regimen used by the Prius is suboptimal and results in the battery being only partially-charged much of the time, which leads to sulfation damage and premature battery death, and the AGM alternative battery is much more resistant to this than the old flooded plate style construction of the OEM battery..