It does not disconnect automatically.
First, if the battery car is fully charged and the charging device is not removed, it will not automatically power off, the charging device will continue to charge the battery, but the charging device has a protection device, which automatically breaks the main charging device after full, and enters the floating charging state.
Second, the so-called floating charge is to switch to a small current to continue charging the battery after the battery is full, which is called floating charging, also known as trickle charging. The small current is generally not artificially set, but after the voltage is set to the floating charge voltage (such as the 12v battery, the floating charge voltage is in the range of 13.2v ~ 13.8v), the battery is fully charged and can accept the current is very small, and the floating charge flow is automatically formed.