keep car – AAA Northeast’s Car Doctor says you should never change or disconnect a car battery with the engine running. The preferred shop method is using a full-size jump pack connected to the ground terminal and the positive cable, insulating the connection, then disco
A battery swap sounds like a simple errand until you remember what’s sitting behind the scenes—your car’s computer settings. One reader asked how to keep those settings from resetting while replacing a battery. and AAA Northeast’s Car Doctor answered with a firm warning: it’s never a good idea to change or disconnect a car’s battery with the engine running.
The question focused on whether a workaround could help. Instead of leaving the engine running, the reader suggested attaching a trickle charger or another 12-volt device to keep the computer settings alive. AAA’s response was specific about what can and can’t be relied on.
“Some of the trickle chargers use the battery to regulate voltage. ” the Car Doctor said. explaining that setup “may not work to maintain the vehicle’s electronics memory.” The guidance turns practical from there. Some advanced battery chargers include a “supply” mode that maintains constant voltage to the vehicle’s electrical system while the battery is disconnected. Portable jump starters can also help: some include a specific 12-volt output mode designed for that purpose.
At AAA, the usual approach during a battery replacement is to use “a full-size jump pack to maintain memory.” The method is detailed: the jump pack is attached to a ground terminal and the positive cable, the connection is insulated, and then the battery is disconnected.
The reader also asked whether a smaller. more everyday setup could work in a pinch—using “a 12-volt cordless tool battery and jumper wires” to maintain the computer memory. The Car Doctor said yes. but reiterated the bottom line: “it is never a good idea to change/disconnect a car’s battery with the engine running.”.
That strict caution matters because the reader’s original instinct—to keep the car’s systems powered without actually running the engine—runs into real electrical details. If the voltage regulation isn’t set up correctly, the electronics memory is the first thing to lose stability.
For drivers who are also dealing with the small, stressful surprises cars throw up right after service or during routine operation, the same Q-and-A runs into other common questions.
A 2026 Subaru Forester owner noted that the engine starts at 1,500 RPM and, after a few minutes, drops to around 650 RPM. The Car Doctor said the elevated idle speed during startup is normal and part of the engine’s cold-start strategy. The car “should be good to drive once all the warning lights on the dash turn off. regardless of the idle speed. ” and the recommendation is to avoid hard acceleration for the first few minutes so vital fluids can circulate.
In another case, a Land Rover Defender key became deactivated. The Car Doctor said keys “rarely become deactivated on their own. ” because they are electronically programmed—though it is still possible if someone was trying to reprogram the key or the vehicle. The Car Doctor added a scenario that can sometimes trigger trouble: if the fob is left in the car for an extended time. To reactivate a smart key. the vehicle must be started using another activated smart key. or the vehicle must be unlocked and locked using the InControl Remote App. The Car Doctor also recommended checking or replacing the fob battery if it is more than a couple of years old.
For maintenance planning, the advice shifts to brakes for a 2011 Ram 1500 needing both front and rear brake pads and rotors. The Car Doctor said factory parts are “always a good way to go. ” but pointed out the cost reality: the original equipment brake pads have a list price of $182. while a quality aftermarket brake pad is less than half that cost. Brand suggestions included Akebono brake parts being used by many shops. with PowerStop pads and rotors used on the Car Doctor’s own vehicles “and had good luck.” The Car Doctor also named traditional brands—Wagner. Bosch. and Raybestos—as makers of good-quality brake parts. On pad type. the Car Doctor said both semi-metallic and ceramic fiber are good: ceramic pads are generally quieter and produce less dust. while semi-metallic pads tend to provide better heat dissipation and braking performance under heavy loads or towing.
And for a 1998 Buick LeSabre inherited with an unpredictable horn problem—where the horn sometimes remains on after the driver removes their hand and on occasion activates without pressing—there are three parts involved: the horn switch. horn relay/wiring. and horn. The horn switch is integrated into the driver airbag module, part of the airbag cover. A first guess is to replace the horn relay. located in the fuse box in the engine compartment; the horn relay is a standard part and easily sourced. The harder-to-find component is the horn switch/pad. Online, the GM part has been discontinued, and a used part from a salvage yard may be the only option. The Car Doctor added that these horn pads have been known to distort over time and cause “phantom horn activation.”.
John Paul is AAA Northeast’s Car Doctor. He has over 40 years of experience in the automotive business and is an ASE-certified master technician. E-mail your Car Doctor question to [email protected].
car battery replacement computer memory trickle charger supply mode jump pack AAA Car Doctor smart key Subaru Forester idle RPM brake pads rotors Buick LeSabre horn