Yes, you can train without connecting the battery charger to your TrueBike, but we recommend to use the battery charger for every training. Depending on the type and intensity of your training, the TrueBike will use more or less power. You will get a warning when the battery is low, but if this occurs during a workout, you do not want to have to get off the bike and find the charger. To prevent having to interrupt your training, please connect the charger at all times.