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I have a battery tender that plugs into an electrical outlet in my garage. It uses a "lighter plug" to plug into the car. I use the console outlet for this. The purpose of the battery tender is to keep the charge level of the car battery topped off.
A memory maintainer is not going to keep your car battery from discharging over time. The purpose (if I am talking the same device) of this device is to prevent components that depend on current being available to maintain memory from being deprived of this current while you disconnect the main battery.