Replacing the 12V battery

[TucsonPrius]

After changing the oil and rotating the tires on my '04 Prius, I noticed that as I filled the last tire, my 12V compressor was quite slooowww. Right about that time, I looked in the car and on the MFD I had the "parking pawl problem" error on the screen. Shutting off the compressor eliminated the error. Knowing that this error shows up on the MFD when the voltage of the Prius is low, I quickly checked the voltage: 11.8V. That was without any accessories.

Now here in Arizona, I've never before had an auto battery last more than 3 years, and this one was 4.5 years old, so I knew it was only time before I get in and nothing would happen (typical failure from the heat is: works fine one day, completely dead the next), so I went off to pick up a new one from the local Toyota dealer.

Cost out the door, including tax was just shy of $150.00; a bit on the pricey side, but when you have nearly a monopoly on the market.... I know one can use an Optima battery with a adaptor kit, but I didn't want to have to deal with that.

The replacement was straightforward, if you want to do yours one day you'll need: 10mm socket, a 6-inch extension, and a ratchet (or equivalents)

First, I removed the negative terminal from the body. This is far easier than trying to remove the cable from the battery while the battery is in place. I then placed a small plastic bag over the cable and secured it with a rubber band; I didn't want it to accidentally contact anything or short out.

Second, I removed the cover over the positive terminal. This is a bit tricky as there are three places where it snaps in place. Remove the positive block from the battery terminal and move it off to one side.

Next, I removed the small vent hose by pulling it straight out. I seemed to recall in the manual that it should not be twisted, so I didn't.

To remove the hold-down bracket, first remove the nut closest to the body wall, then using the 6-inch extension, remove the one between the battery and the brake capacitor. I did this one so I could remove the screw along with the bracket to prevent dropping it.

Now the battery is free, but I wasn't able to pull it out easily, so I removed the small piece of vent work right near the battery. This is held in place with two screws: one attached to the floor and one to the side of the compartment. Once this is removed the battery can be pulled up and out.

After removing the battery, I took the negative cable off the old battery and placed it on the new -- double and triple checking that it was indeed the negative post -- and reversed the steps to put the new battery in place and reconnect.

All told, from start to finish took me about 30 minutes and was really easy.

Thanks,
Shawn

[Patrick Wong]

Originally Posted by TucsonPrius

...Second, I removed the cover over the positive terminal. This is a bit tricky as there are three places where it snaps in place. Remove the positive block from the battery terminal and move it off to one side.

...double and triple checking that it was indeed the negative post -- and reversed the steps to put the new battery in place and reconnect.

Hi Shawn,

Congratulations on your success. Regarding the positive terminal cover, I have found that it is quite difficult to remove. However it is unnecessary to remove it if you just bend the cover back enough so that you can access the terminal nut.

It is a great idea to ensure that the replacement battery has the same terminal polarity as the original. Especially for 2G Prius without SE/SS, the battery size and the case cosmetic appearance will be the same as the Classic battery; but the battery terminal polarity is reversed. It is not impossible to visualize how a Toyota dealership parts clerk might by accident sell the Classic battery for use in a 2G base model; or the reverse.

[richard schumacher]

Would you say it is feasible to connect the new battery to the electrical system with alligator clip wires before disconnecting the old battery, so as to preserve system settings?

Did you typically use accessories with the car not ON/Ready? That can shorten the life of the 12V battery.