Actually, there are a few things about the Prius 12v. 1) The posts are JIS (I THINK that is Japan Industrial Standard??), which means the posts are not as wide as the typical battery. 2) The battery is AGM (Absorbed Glass Mat), which is not all that unusual nowadays, but... 3) The battery sits inside the passenger compartment, so it has a special vent hole on the side, which a small tube connects to direct any off-gassing to the exterior of the vehicle. 4) The battery does not turn over the engine as do most 12v auto batteries. It basically powers up the computer and other "gizmos" so the car can start -- so cranking amps are not a big deal. Can you buy one at WalMart? Sure if they have AGM batteries of the proper size (has to fit in the space) with JIS posts and the proper venting system as well as the specs needed. A quick check of WalMart's Web site shows they have only one battery that fits.. Local stores may differ. Personally, I would go the dealer (looks for parts coupons on the dealership web site....or go on Saturday and beg for a weekend discount)> Here's only choice WalMart offers: OPTIMA YELLOWTOP YEL DS46B24R-WM 3 Years Free Replacement 450 CCA (Cold Cranking Amps) Available on walmart.com only $237.99† View Online More Info
25 miles to the dealer and no major elevation changes. For the last month my mpg has been 45 or under. Each time I've reset it, I've not seen it get over the 45 mpg level for any 5+ mile distance and driving as I usually do. Returning from the dealership, I averaged over 47 mpg and that was with the AC on as it was over 80 deg today. So I do believe the higher mpg is the result of the battery change.
Further to what @cyberpriusII was saying, even with an Optima Yellow Top, supposedly the correct size, when I installed one, it was maybe a millimeter taller, and that was enough cause the hold-down bracket to rock, needed a washer shim at one end. What a goofball design from Toyota btw, to be that intolerant of small variation. The traditional design of bracket like this: Accommodates a decent range of width and height variation.
Out of interest, why do you say its highly unlikely that the bump in mpg that I noticed is not real? Just got back from a 20 mile drive and mpg is holding at just over 47. I haven't seen it at over 45 in months and I've also read other accounts that have claimed an increase in mpg after changing out the 12V.
I said that in my first post on the subject. The onboard MPG calculation is notoriously unreliable, especially over short distances.
Well, I'm at about 50 miles and as mentioned I haven't seen my display read over 47mpg for months (and I've reset it multiple times). So I think its fair to assume the increase in mpg is due to the battery change, but I agree that more miles are needed to get a more accurate reading.
Didn't read the whole thread so apologies if already mentioned but the 12 volt battery back up box in the back thats connected to the 12 volt buss if its gets some bad caps it will slowly deplete the 12 volt battery. Just saw one recently and another poster mentioned it. I think I have seen maybe 3 of those go bad.
In this regard, I wouldn't pay to much attention to the view of someone who does not have and never has had a Prius Gen 2. It can make a difference if the battery is constantly low, whether that is from not being driven enough, the battery is old and failing to hold (enough) charge or other reasons. If the old battery had a shorted cell, you would definitely see an improvement. Look into the "Ignore" feature, if ever you find a particular poster is too rude or argumentive.
