Replacing Battery in Late Model Subaru

I’m going to replace the batter in my 06 Outback Sport tomorrow, The one in there now isn’t dead, but a bit weak on cold mornings.

My question has to do with what happens when you take the power off of the car’s computer systems? I know I’ll have to reset the radio presets but what I’m really concerned about is what happens to the electronic throttle modulator and other important settings. I’m surprised the owner’s manual doesn’t go into more detail on this.

You will loose all that is stored in the RAM modules inside the computers - depending on the size of the storage capacitors in the boards. In some cases that means the trouble codes and pending codes in the powertrain controller module and basic settings, but all electronic controller should default to factory default. Just make sure you follow safety procedures during removal and installation, some of your parts are not replaceable…

Okay, thanks. Then is there a way not to lose that info? If I hook a batter charger to the battery terminals before I remove them and keep them there while until the new batter is in and hooked up, that information should not be lost?

How does the Subaru dealer replace a battery?

I am sure the mechanics at the dealership don’t worry about changing a battery like we do…they do it all the time and we just worry about doing it correctly… … Also, if the car is running fine why would you need past codes?

Walmart sells a device that you plug into the cigar lighter that keeps all settings, probably have at all of the auto supply stores too, it is not expensive, it will be a lot safer than trying to use a battery charger!

Here’s what I use when disconnecting batteries from late model vehicles.


I would NOT use a battery charger to keep things going while I removed the battery. The chargers are usually just rectifiers – no filtering, no voltage regulation. They rely on the battery’s being there to keep things right. Without the battery you will have recitified AC, which will probably not work to keep the computers going, and you risk overvoltage, which might damage some electronics.

Instead, use the little power outlet adapters suggeted below (but I wish they would be set up for 12V instead of 9V).

Assuming we are only talking about the car and not any accessories like a phone book,It should not be that much of an inconvenience. Your engine control module will reprogram the engine settings and you will be back to normal in a few miles of driving.

Yes…you may have to reprogram your radio and some other fancy electronic stuff. On my car, which is a 96 Ford, I changed the battery this week end and the radio presets did not get lost. I don’t know exactly why and I won’t try guess here. It started up on AM which it normally won’t because I never listen to AM but all the presents were still present.

Here’s why I use a back-up power supply when disconnecting batteries. On some GM vehicles when the battery is disconnected some modules go to sleep and never wake back up. Then it’s off to the dealer to have the module(s) replaced and a reprograming performed. Much cheaper to just use a back-up power supply.


This is simple. Leave your headlights on all night. In the morning you will have a dead battery. That is what will happen when you remove the battery. This is an everyday problem; you haven’t really made your concern clear. Why is your situation different?

From a discount store, purchase 2 six-volt lantern batteries. You will also need 3 light “test wires” with alligator clips on both ends. Use one wire to connect the two batteries in series, producing a 12 volt dry cell battery. Connect the positive terminal to the positive battery cable in your car. Same for the negative. Now you can disconnect the cables while maintaining 12 volts on the cars electrical system.

The exact same thing can happen if a battery goes dead in a late model vehicle. This ain’t 1996.


“Here’s why I use a back-up power supply when disconnecting batteries. http://www…safety.htm. On some GM vehicles when the battery is disconnected some modules go to sleep and never wake back up.”

I just looked through that website and I am astonished. I have never heard of battery removal causing such issues; that just seems like horrendous design. Here are some more issues brought up (can anyone verify if this all is true?):

  • Chevy Tahoe Loss of voltage to the vehicle electrical system causes the 4WD module to go to sleep permanently. The module never wakes back up when power is restored, and the only way to restore normal 4WD operation is to replace the module with a new one (a repair that may cost you over a hundred dollars!).
  • Mercedes (various models) Loss of voltage to the vehicle electrical system will prevent the A/C from working. The climate control module must be reset to restore normal operation. It may also disable the Stability Control System. The ABS module has to undergo a relearn procedure for the steering angle sensor to restore normal operation.
  • Toyota (various models) If the battery is disconnected while the key is on, it can set a fault code for the airbag system and turn on the airbag warning light (which deactivates the airbag system until the fault is cleared with a scan tool).
  • Subaru (various models) Disconnecting the battery can trigger the anti-theft system, preventing the vehicle from starting when the battery is reconnected.
  • Saturn L-Series The body control module may forget the odometer display reading. Nice if you are selling a car and want a 0 mileage reading, but expensive to fix because it requires replacing the BCM (at a cost of $300 to $400) and reprogramming the odometer reading.
  • Honda (various models) Disconnecting the battery will set a code and turn on the air bag light (which also disables the airbag system). The dealer must reset the system with a scan tool to restore normal operation.
  • BMW, Audi & VW (various models) Disconnecting the battery requires numerous module relearn procedures which can take up to several hours with a factory scan tool

You only need 5 volts to keep computers and modules alive.