Read the instruction. The answer can be yes or no depending on what you want to undertake with the charger.
If the battery is completely flat and you want the charger to enter recovery mode then the battery needs to be disconnected. The device will be programmed to detect when it is connected to a load and will not enter recovery mode as this can damage the bike's electronics.
If you want to only use the maintenance mode e.g. to keep the battery charged as you have a drain such as a tracker or alarm then you do not need to disconnect the battery as recovery mode is not needed for this application.
