If your product does not have a battery, you need to use your charger to power your bike. But if you have a battery, it can, in certain cases get drained even if you are cycling, such as long interval sessions or climbs. So, since your bike will not draw energy from the charger in most cases, we recommend you keep the charger as a backup for more extreme loads.
Important: It is paramount to keep your battery well-conditioned by keeping it sufficiently charged. If the battery is completely drained for prolonged periods of time, it will be irreversibly damaged. This means that the device should be connected to a power main at least once every two months. Especially if you don’t use your device for prolonged periods. Damage to batteries due to bad conditioning of your battery is not covered by warranty. See the full warranty details here.