I have the original Prius, which uses a 12 volt battery with a vent to the outside because it is located in the trunk. Toyota no longer sells the original battery. It sells an upgraded battery and a kit which together with the labor cost can amount to $300.
Owners find this price a little hard to take. Were it not for the vent, one could use an off the shelf battery which sells for less than $100. At least one owner has reported on the net that this is what he has done. Is this a dangerous practice or was Toyota being extra cautious in using a vented battery?
It was on a Prius forum that this question arose. Those discussions involve opinions. I want a definitive answer from an authoritative source.
So, who’s “authoritative” enough in your book? If you ask Toyota, I’m sure they’ll tell you to use only the expensive OEM solution (they’re just covering their butts). If you ask anyone else, it’s an opinion.
That said, I gather that this is a normal 12V battery in a poorly ventilated area (trunk), and Toyota has some sort of vent to the outside to prevent hydrogen gas from building up (you don’t want your car turning into the Toyotenburg!). So, if it were me, I’d use a regular battery and just make sure that something is done to ensure adequate ventilation. Was the original a passive vent, or did it have a powered fan to blow outside air into the battery compartment? Did something cover the vent caps to capture the gas*, or just a vented box? Just make sure to do whatever is necessary to ensure that anything the battery gives off vents to the outside, not into the trunk or passenger compartment. The rest, and the responsibility for doing it right, are yours.
- Hmm. People pay good money for systems to generate hydrogen from water and feed it into their engines… (yes, I know it’s not energy or cost effective, so let’s not go there…)
Check with the battery companies. On line and maybe in person locally. There are other cars that have that kind of vent system. I would have to believe they are likely to have batteries available other than through Toyota, after all Toyota does not even make batteries, they just have their name put on them.
I had a Miata that had a trunk battery that had it’s own vent, my motorcycle has a vented battery and if I recall correctly my sunbeam Imp’s battery also had a vent to the outside. I never had problems finding replacement batteries for them.
The usual alternative to the Prius battery is the Miata battery.
Now that I remember back to my '71 SuperBeetle, its battery was under the back seat, with no special venting. Of course, in those days, manufacturers didn’t have to worry so much about product liability suits…
Now that I remember back to my '71 SuperBeetle, its battery was under the back seat, with no special venting.
Yea, I had a 1970, but if you got a heavy weight in the back seat and the springs in the seat hit just right, I understand it could be a very inspiring moment. 
A special feature on VW’s bugs, the seats were so poorly held to their tracks a rear-ender whould cause the seat to pull out of it’s tracks and the back of the drivers head would hit the seam for the rear window. Things got a little better with the SuperBettle. How about that “special” fuel hose and the pump shooting directly at the distributor
Some other place might sell the Prius battery. I think I saw vent tubes on batteries at Sam’s Club so it may be possible. I think you could take a chance on a maintenance free battery but I don’t know why Toyota thinks the Prius battery should be different.
All my BMWs have batteries in the trunk. The battery I use (group 48 or 49?) comes with a vent tube. I just replace the original short hose with a longer nylon tube, drill a hole where rain water won’t force its way up into the battery box, and run the nylon tube out my hole. Paint around the drilled hole and use a rubber grommet to give it a factory quality job. It has worked fine so far on the two cars that I have done it on.
It is not just the vent tube but the size of the battery that is different in the Prius. The upgrade kit that you must now buy from Toyota is because Toyota sells a different size battery to replace the original.
$300 sounds like a reasonable price to me for a replacement hybrid battery.
This is not the hybrid battery, it is the same 12 volt battery used in all cars.
In that case, you are right.
Shop around. You should be able to get a non-OEM replacement that is the same size and install it yourself.