There are three main types of UPS systems, categorized by how the systems work: standby, line-interactive, and on-line. Standby UPSs provide basic protection from power problems, correcting blackouts and brownouts by switching to battery power. A Line-interactive UPS provides a higher level of protection from power problems, correcting brownouts and overvoltages without using battery power. On-line UPSs provide the highest level of protection from power problems. The on-line UPSs continually remake incoming AC power, completely isolating connected equipment from power problems.