I have only ever replaced the 12V battery while the car is on a lift, and I would strongly discourage anyone from attempting otherwise. (Any mention of “battery” in this article refers to the conventional 12V lead-acid battery.)
Lee Underkofler was kind enough to make this suggestion for those of you attempting this repair without a lift: Remove the front bumper cover. It’s relatively easy to do. I’ll try to remember to put up some instructions and photos– If I haven’t deleted this sentence by October 2015, someone please prod me to do an update.
Here is a document provided by Think regarding 12V battery replacement:
But I’m still going to provide my own advice:
The battery is located under the car just inboard of the left front wheel. Remove the entire battery bracket assembly, install a new battery into the bracket and then reinstall the bracket to the car.
When 12V power is disconnected from the car, radio presets, settings and clock will be lost, but otherwise no relearning procedures are required. (With some conventional cars there are special procedures to relearn throttle position, idle speed, power window positions, etc after 12V power is disconnected.) I would discourage trying to maintain 12V to the car through the Data Link Connector or accessory power port in the passenger dash while the battery is being replaced; there are many opportunities to short 12V to ground during the process.
Lift the car.
Disconnect negative battery cable from the battery using 10mm wrench (I have been unable to fit a ratchet or ratcheting wrench on the nut). Be careful to not create a short circuit between the positive and negative post of the battery. There should be a plastic protective cover on the positive terminal, but this is often missing.
Install a cap on the negative post of the battery to prevent an accidental short circuit. If you don’t have a spare one handy you can probably take it off the new battery. Just be sure to move the caps back to the new battery before you start installation.
Disconnect the positive terminal from the battery. If there is a plastic cover on the positive terminal, remove it by gently pressing the three tabs (one tab visible on the right, two not visible on the left side of the cover). Loosen the ny-lock nut with a 10mm wrench or ratchet.
Install a cap on the positive post of the battery to be thorough about preventing a short circuit.
The bracket is installed to the frame of the car by one bolt (left, forward and just above the battery itself) and two nuts (above the aft end of the battery). They usually take 13mm wrenches/sockets (deep sockets required for the nuts), but I have also seen nuts/bolts that require 12mm tools.
Leave one of the nuts threaded on a few turns until you are ready to support the full weight of the battery/bracket assembly. Remove the nut and lift the battery/bracket forward, off the studs and down to the floor or onto a bench.
Before removing the bolt, note the orientation of the small bracket on the left that secures the battery into the large bracket assembly. Its orientation was a little bit counter-intuitive to me the first time I saw it. Remove the bolt with a 10mm tool.
Install a new battery into the bracket and secure it with the bolt and clamp. (The brand of battery that we use at Hawthorne Auto Clinic has a small bit of plastic that interferes with the bracket on the right side, so I just cut it off that tiny bit with a utility knife.)
Important: Make sure caps are installed on the positive and negative posts of the new battery!
With the battery removed from the car use a wire brush to clean the positive and negative battery clamps. I haven’t seen any corrosion/gassing/leakage damage on these clamps like I so often do in conventional cars. I have to suspect that such damage in conventional cars is due to the higher temperatures in close proximity to internal combustion engines. I suppose that it also could be due to charging by an alternator rather than a DC-DC converter. Or the much greater electrical current that is briefly required to start an engine. Anyway, all I want to say is that you probably won’t need to clean the clamps with baking soda and water or any similar fancy cleaning solution.
Loosen the clamp nuts fully and use a terminal spreader or similar to open the clamps up so that you’ll be able to seat them as far down on the battery posts as possible.
Tuck the battery clamps and cables up and out of the way so they won’t interfere when you’re trying to get the battery/bracket assembly back in the car.
Watch out for the windshield washer hose which traverses this area all willy-nilly. I’ve gotten it pinched between the battery bracket and the frame, cause a leak, and made plenty of extra work for myself to get it fixed. Tuck it out of the way or even secure somewhere that it won’t be in the way.
Pro Tip: The first time or two that I replaced a battery in a Think I was a sweaty frustrated mess before I was through. Here’s what made the difference: Locate the bolt the secures the negative battery cable to the frame. (It also secure the ground strap for the PCU to the frame.) Loosen the bolt so the ground cables/straps can be rotated forward, away from the left stud on which the battery bracket is mounted. The bracket has to fit behind those cables/straps which makes for a very narrow window to get onto the stud. Don’t forget to re-tighten the bolt when you’re done.
With one nut in hand lift the battery/bracket assembly overhead and guide the right bracket hole onto its mounting stud. Thread the nut on a few turns, and it’s safe to let the battery/bracket assembly hang without your support.
Get the other bracket hole onto its mating stud and fully install the two nuts and one bolt.
Remove the cap from the positive battery post, install the positive clamp/terminal and tighten the nut just enough so the clamp can’t be easily twisted on the post.
Install the plastic protective cover on the positive terminal if one was initially present.
Install the negative clamp and tighten the nut. The negative cable probably won’t be in the exact same orientation as it was with the Varta battery, and that’s okay. A small spark when connecting the negative clamp to the battery post is normal.
Reprogram your radio with the correct time, presets and setting (and please turn off that annoying demo mode!).