When PLC program to keep in RAM when used batteries, the battery usually 3V or 3.6V non–rechargeable lithium-ion battery, battery life is usually about five years or so, the battery is used for a long time, the voltage will drop, when it dropped to less than to ensure that the data in RAM, the program in RAM is lost. If the user does not have backup procedures, be cumbersome.
General PLC has battery voltage detection circuit when the voltage drops to a certain extent, PLC will alarm, reminder to replace the battery. PLC manual replace battery. In General, the PLC after the power outage, because RAM in the PLC power supply terminal charging capacitor, even removed the battery, capacitor charging power RAM enough data for some time, so if you take out the battery for a short time (usually 5 minutes) then a new battery changed, the data is not lost. But they actually use the PLC‘s different environmental conditions, such as declining capacity of the capacitor, RAM power supply circuit discharge circuit such as dust, sludge and other formation, which would speed up the PLC after the power capacitor discharge speed, allowing time to grasp. If charged in case the battery replacement procedure foolproof. Because the power will always have voltage on the RAM chip power foot. Of course, also be careful when replacing, pay attention to the polarity of the batteries and to avoid short circuit occurs.