Editing Lead (section)

=== Batteries ===
The largest use of lead in the early 21st century is in [[Lead-acid battery|lead–acid batteries]]. The lead in batteries undergoes no direct contact with humans, so there are fewer toxicity concerns.{{efn|Potential injuries to regular users of such batteries are not related to lead's toxicity.{{sfn|Concordia University|2016}}}} People who work in lead battery production or recycling plants may be exposed to lead dust and inhale it.{{sfn|Toxicological Profile for Lead|2007|pp=5–6}} The reactions in the battery between lead, lead dioxide, and sulfuric acid provide a reliable source of [[voltage]].{{efn|See{{sfn|Progressive Dynamics, Inc.}} for details on how a lead–acid battery works.}} [[Supercapacitor]]s incorporating lead–acid batteries have been installed in kilowatt and megawatt scale applications in Australia, Japan, and the United States in frequency regulation, solar smoothing and shifting, wind smoothing, and other applications.{{sfn|Olinsky-Paul|2013}} These batteries have lower energy density and charge-discharge efficiency than [[lithium-ion battery|lithium-ion batteries]], but are significantly cheaper.{{sfn|Gulbinska|2014}}