your SLC 500 and PLC-5 have a consumable part in them and most plants have no PM task for it

every legacy AB processor still running out there has a lithium battery in it holding the program in RAM. 1747-BA on the SLC 500 side, 1770-XYC on PLC-5 (some older PLC-5s take the 1770-XYB, check yours). rockwell rates the SLC battery around two years on a 5/02 through 5/05. plenty of the ones i get asked about have been in a lot longer than that.

three things worth knowing.

the BATT / BAT LOW light is not a warning with weeks of margin on it. it means below threshold, and on the SLC there is a status bit that sets at the same time (S:5/9). if you are not alarming that bit into your HMI then you are relying on somebody walking past the rack and looking at it.

swap the battery with the line power ON. this is the one that bites people. pull it with the rack powered down and there is nothing holding the RAM, and the program is gone. that turns a cheap consumable into a multi day outage, every time the only copy of the program was the one living in the processor.

which is the actual point. the battery is not the risk, the missing backup is. if the program only exists in processor RAM then a five dollar part is a single point of failure on the whole line. an EEPROM or flash memory module in the CPU memory module socket carries the program independent of the battery, and a copy of the .RSS or .RSP file sitting on a machine that actually gets backed up costs nothing at all.

if you run legacy racks, worth doing this week: walk them, write down which ones are showing BATT, and find out whether anybody can actually produce the program file. the number of plants where the honest answer is "it is on a laptop that retired with jim" is higher than you would think.

anyone running PLC batteries on a real PM schedule, or is it run to failure pretty much everywhere?