Lifetime Of Batteries Used With The MicroLogix 1500. Question Lifetime of Batteries used with the MicroLogix 1500 Answer 1) What is the expected lifetime of the permanent,(not replaceable) battery? The expected lifetime of the permanent battery is (7-8) years under normal operation. The word normal is important. Extreme temperatures and other environmental conditions can shorten the battery life. 2) What is the expected lifetime of the replacement battery,(1747-BA)? If the replacement battery is added when the primary battery is close to the end of it's life an additional 3-5 years of life will be added. If the replacement battery is added when the processor is first installed, an additional 1-2 years of total life will be added 3) What is the function of the (2) batteries in the processor? The permanent battery is permanent. It is meant for memory backup. If the lifetime of the processor exceeds the permanent battery lifetime then a replacement battery, (1747-BA), can be installed to retain memory. The replacement battery can be installed in order to extend the total life. The batteries are wired in parallel with diode protection between them. 4) What is the expected lifetime of the battery in the RTC module? Both the 1764-RTC, and the 1764-MM1RTC, use a battery that cannot be replaced. The expected lifetime of this battery is (5) years.