Radio turns on when car starts



Ignition off current has been something OEMs have focused on for decades, they want a customer’s car to be able to sit somewhere for at least 30 days and not have a dead battery. That is why most telematics systems turn off the cell modem after 14 days of no activity, to conserve power longer to still be able to turn over the engine in several more weeks.

They use the CAN bus and ignition/accessory states very well to control off current draw. There is absolutely no reason in a modern vehicle to be concerned about possible battery drainage for anything other than lights or if there is an always on 12V outlet with something plugged into it. I don’t think the Ascent has an always-on (non-accessory) outlet. If a component in a car stays on in the true off state (after all timeouts) it is either a light that was intentionally left off of the BCM control or it is malfunctioning, or a door/liftgate switch is open and they didn’t implement a timeout for that condition. Some exceptions come in with variance from OEMs, but what I said is fairly typical.

The only realistic concern is any accessories plugged into 12V accessory outlets. Even modern alternators/batteries can allow states that send transients and spikes which could damage a device, but most accessories have adequate filters, and those issues are usually with a failing battery or alternator. The most severe circumstance is when jump starting a vehicle and a few things that can happen at that time, I personally recommend unplugging accessories when jump-starting, and to minimize current draw turning off everything that can be turned off. All installed components in a vehicle are designed and tested to have immunity to transients, spikes and noise. Reverse polarity, high voltage, etc. should blow a fuse as a worst case and not damage a component.

All that said, I think whatever user controllable state you leave the vehicle in is the state it should come up in.

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