It will work fine. You don't even need a "large back up battery"... I have an equivalent "dongle" that just uses a 9v battery. Make sure that nothing is plugged into any of the lighter outputs and the ignition switch is off. I have changed vehicle batteries that has taken an hour or so and things were fine there after with all radio settings save and no "banging" of vent actuators.I want to avoid the HVAC actuators recalibrating. Will this be sufficient?