1, you said that \"there is a three-hole socket under the cushion\" this socket is used for charging, that is, the so-called input port. The charger is connected to the power supply (220 AC, AC is no direction, positive and negative plug are the same), and the other end is plugged into the \"charging of this three-hole socket\" that is, the positive and negative poles is right, do not worry. Because the AC after the charger, it has a \"bridge rectifier circuit\" inside will automatically convert the AC to direct current corresponding to the battery, and now the plug like the line in the computer will not plug back, because the plug is simply not plugged in.
2, about the output outlet in the battery inside there is a plug connected with the battery, that is, on the battery box. Just plug in the cable that powers the electric car.
3, normal use if you do not take out the battery, directly use the \"cushion under a three-hole socket\" charging normal use.
4, if you can use a multimeter is simple, in the charger to charge the electric vehicle that plug with a multimeter DC voltage file to measure the voltage, write down the positive and negative electrodes, and then measure the electric vehicle charging plug to note the positive and negative electrodes, must be corresponding, not to be sure. I hope it was helpful.