These type of UPS systems are of basic design. It provides limited protection in that any voltage variations or spikes are not regulated or filtered adequately. The units only switch to battery backup mode after detection of power failure, usually 5-10ms later. Some sensitive loads may require better voltage stabilization, hence choosing the correct UPS is important. Offline UPS systems are usually cost effective as they have less control circuits and ability. Your backup time is limited to minutes as they include one or two batteries at most. An offline UPS does not have the ability to connect additional batteries as the charger has limited power, should this be done your batteries will not charge resulting in premature battery failure. An offline UPS is only effective in applications if power failure occurs once or twice a week for 5-10 minutes.