The most important thing to maintain for a hopfällbar elcykel is a battery. It is best to discharge and charge the battery at regular intervals. Usually two or three weeks. This can activate the capacity of the battery, so that electric bicycle run more time.
If you have bought foldable electric bike in the last year or two, they should be brushless self-charging electric bike motor. Brushless motors do not need to be maintained. But if they were bought earlier, some of them might be brushless motors. And brushes the motor if want to maintain, can disassemble the rotor to use the lathe plane copper head, plane to copper hair bright. Then there is the carbon brush. If the length of the carbon brush is less than the original 1/3, the brush needs to be replaced.
Brushless motor to avoid water. Brushless motor is afraid of water, the water will burn; brushless motor better, but if the water is more, it will also affect the life of the motor. So rainy days had better not open out.