When I had the PPI done on my car, the most major item noted was that my car's battery failed a load test. It hasn't seen too many miles in the last month, since I bought it, so I had delayed dealing with replacing the battery until this weekend.


In searching the forums for info about batteries recommended for our cars, there was a wide divergence of opinion. Since the 996 is a new platform to me, I was looking for basics - BCI Group size, CCA, etc.


I figured what better source for reliable info than the Battery Council International ("BCI") since it is the worldwide organization that develops and maintains standards for batteries? I've attached two documents. The first is the BCI Battery Reference Chart, which definitively answers the questions I know I've had about battery "group" sizes and how they cross-reference to battery "H" sizes. A very useful chart IMO. The second document is the official BCI group size listing for 911 models dating back to 1998. Note it only covers the group size, not the specified CCA for the particular application, so always check your owner's manual.


Anyway, I learned the 996TT uses a Group 94R battery, which is also known as a "H7" by its DIN code. The Turbo spec calls for 800CCA, which is uprated from the base battery spec for the 996.


Now here's the good news. I found two minimum 800CCA AGM batteries that come with a 4 year free replacement warranty (the rest are primarily only 3 year warranties) - the Bosch 94R AGM sold by Pep Boys, and the AutoZone Duralast Platinum H7 AGM, which is actually rated at 850CCA. The even better news is that Pep Boys is currently running a promotion on batteries, and I was able to snag the Bosch battery for 25% off regular price. There may be other similarly rated AGM batteries out there, and I know not everyone has an interest in spending a bit more for AGM technology (which Bosch developed incidentally).


I installed the Bosch battery this afternoon; took maybe 5 or 10 minutes tops. Remove the battery cover. Disconnect the negative ground cable first. The disconnect the Positive cable. A 10mm socket does the trick. Unplug the vent line from the battery. Using a 13mm socket, release the retaining bracket at the base of the battery on the passenger side. Lift the battery out of the vehicle. Installation is reverse of above. When you set the replacement battery in place, make sure it sits correctly on the battery tray and that the lip of the base is under that retainer on the tray. Install the retaining bracket and torque to 27 Nm. Plug in the vent line. Connect the negative cable first and torque to 5 Nm. Then connect the positive cable (same torque spec), reinstall the cover, and you're essentially good to go.


The extra capacity of the Bosch AGM was immediately apparent compared to the tired lower CCA existing battery when I fired it up for the first time. Glad to be able to cross another prior owner "deferred maintenance" item off the list.

 

Reads like the process went well for you. In some cases a steering sensor error can be triggered. This will go away on its own if the car is driven.

Any time the power is removed the windows should have their limits reset. The procedure should be in the owners manual.

From memory: Press the lower button until the window is all the way down. Release the button. Then press and hold the raise button until the window is all the way up and for at least 5 seconds after. Repeat for the other window.

Also, it is not a bad idea to calibrate the e-Gas system.

Again from memory: With your foot off the gas pedal through the whole procedure turn on the key to the 1st position. Do not start the engine. Leave the key on for at least 60 seconds. If it is quiet where you are you may here some faint mechanical noises which I take to be the throttle body resetting. After 60 seconds turn the key off for 10 seconds. The next time the engine is started the calibration will be complete.

 

I only described the removal / install of the battery. As you correctly note, there are several possible ancillary steps that may be necessary if the battery is disconnected.

These include readaption of the idle speed positioner, throttle, and fuel mixture, all of which the DME will readapt the values automatically after the engine is run for several minutes. For Tiptronic equipped cars, the pressure adaption will be lost possibly resulting in poor shifting. The Tip readapts during the test drive as well (the drive should include different engine loads and speeds to fully readapt the Tip). As noted, the window limit position is lost when the power is disconnected, so they must be reset by closing each window as far as it will go, releasing the switch, and then pressing it to close again. That resets the limit position. The vehicle's clock may lose its time and date which can easily be reset. If the gas tank is low when the battery is disconnected, it may cause the remaining fuel display to be inaccurate. Avoid this by making sure the tank is most full before replacing your battery, but it will self-correct once the tank is refilled. Depending on the year of the car, the radio may require its code to be input following loss of power. If you've lost your code card and have a Durametric available to you, you can read out the code in the DME information section before you disconnect the battery. Finally, the GSP will likely have to reacquire the positioning satellites if your vehicle is so equipped.

Nothing earth shattering here, but some additional details to pay attention to when replacing the battery.