The next point deals with the ability to efficiently extract energy from the source. Different harvesters have different requirements, whether it be matching the impedance, converting the AC source to DC, or tracking the maximum power point, as in solar. An efficient interface which can maximize energy extraction from the source is needed. It does little good to optimize the power converters from 85% to 95% if the interface is not carefully designed. An efficiently designed interface can extract much more power than a poorly designed interface. Next, the energy storage element must be managed. In the case of thin film batteries, they can be destroyed if they are over-discharged, so an accurate undervoltage (UV) detector is critical. Most lithium-ion technologies can create safety hazards if overcharged or exposed to extreme temperatures.