Methods and apparatuses for in-use charging for wearable devices are described, in which the wearable device may include an energy harvesting unit coupled with a rechargeable battery unit. The energy harvesting unit may include one or more transducers configured to generate electrical energy from various types of non-electrical energy around the wearable device such that the wearable device may replenish the rechargeable battery unit while a person uses the wearable devices. Such non-electrical energy may include electromagnetic energy, light energy, thermal energy, kinetic energy, or the like. Additionally, the rechargeable battery unit may include two or more partitions such that one of the partitions may be detached when necessary (e.g., to replace with a fully charged partition) without disrupting operations of the wearable device.