If your battery is completely dead, you're already screwed (technical term) as to your settings.

But if you still have some juice in it, there are small units that you can plug into the cigarette lighter socket that have a battery to provide enough voltage to keep the radio settings. If it will work for your car.

Just be careful lifting that battery, it's heavy. I saw a parts monkey at a Checker darn near kiss the top of one when he tried to pick it up. His upper body moved, the battery didn't. I was able to hold the laughter until I got outside.

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Remember, it's not just a car. It's an Adventure.