If you are stuck with a dead battery and there is a outlet near by, you could carry match box with a diode bridge and a few resistors too slow the charge.
Most cars have a voltage meter on the dashboard to monitor the charge with. You can build this inside a plug outlet, with such low power supplies to the battery it will take some time to get a charge enough to start the car. This is only a emergency supply of D.C. not advised to use make or sell, just a example of how to get there from here. Remember that working with line voltage is dangerous. Test everything twice before applying any current to a circuit.
