When disconnecting battery cables, is it necessary to first connect the cables to a 12 volt source to maintain computer settings etc. I recently had a new battery installed at a Sears shop, they did not do this and said it was not necessary. There were no noticeable problems afterward.
Depends on the car. Toyotas are good about radios and other interior devices maintaining memory so you don’t lose your station presets, etc. Many other cars will lose the clock and radio settings, power seat and steering column memory presets, etc. Cars with an “anti-theft” stereo may go into lock-out mode and not be able to be used until the “unlock code” (given to the owner when the car was purchased) is entered. Guess how many people know where that info is or even have it?
Aftermarket or factory alarms may flash or sound the horn when the battery is reconnected.
Some cars may need to “relearn” idle speed control when battery voltage is lost, resulting in poor or erratic idle speed.
Disconnecting the battery may reset the on-board emissions diagnostic system meaning you may not be able to take an emissions test if you replace your battery immediately before testing.
These are all reasons that a shop should maintain battery voltage during service, but does not mean that any damage can happen if they don’t.
Disconnecting the battery on some vehicles can cause all sorts of problems. If a 5 volt or higher power source is supplied to the vehicle before disconnecting the battery these problems can be avoided. You can read about it here. http://www.aa1car.com/library/battery_disconnect_problems.htm
I agree with the aforementioned advice. The only thing I would add is that I always apply a 12VDC voltage to the cables before removing any vehicle battery. It’s cheap insurance against any malfunctions that may occur in any electronic component on the vehicle.