Battery chargers are used by all residential or commercial devices that are powered by batteries. Battery chargers may be stand-alone equipment, or embedded in other products. Examples of residential devices which use battery chargers include mobile phones and laptop computers. Commercial devices with battery chargers include two-way radios, emergency backup lighting, and lift trucks. Uninterruptible power supplies (UPS) combine a battery charger and a battery with controls to provide critical protection for some electronic devices, particularly computers, which are sensitive to power outages or fluctuations in electricity supply.
In January 2012, The California Energy Commission (CEC) set state-level energy efficiency standards for battery chargers. Standards took effect in 2013 for residential chargers and in 2014 for commercial chargers. In 2013, Oregon adopted similar standards that went into effect in January 2014.
In May 2016, DOE issued a final rule for residential battery chargers with standard levels similar to those in California and Oregon. The standards will take effect in 2018, preempting California and Oregon standards for residential chargers, but not for commercial chargers. Between 2012 and 2016 battery charger manufacturers shifted production to comply with the California and Oregon state standards so that about 95% of residential battery chargers sold nationally already meet the new federal standards.
DOE originally proposed standards for UPSs as part of the 2012 battery chargers rule. However, DOE later determined that a new test method for measuring UPS efficiency was needed. In December 2016, DOE issued a final rule for first-time standards for UPSs. The UPS standards final rule has not yet been published in the Federal Register. The standard defines three types of UPSs and establishes minimum energy efficiency levels that come into effect two years after publication.
DOE estimates that UPS meeting the new standards would save $1-3 billion for US consumers and businesses and prevent the emission of an estimated 49 million metric tons of CO2 over 30 years of sales. (Savings from the May 2016 battery charger standards can be found below left.)
Battery chargers operate in three modes: no-battery, maintenance, and active modes. In no-battery mode, the charger is plugged in but is not connected to a battery. In maintenance mode, the charger is plugged in and attached to the battery, which is fully charged. In active mode, the charger is plugged in and attached to the battery, which is being charged. To ensure energy savings during actual use, it is important that battery chargers be efficient in all three modes of operation since the amount of time spent in each mode varies significantly among products and among users of a given product. Inefficient battery chargers often continue to provide constant current to the battery even after the battery is fully charged.