Siemens S7-300 power supplies

I don't know if this is the right place or not, but here it goes.
I have 16 S-7 300 PLC units, we use them as training stations for students where I work. My question is, since they are turned off most of the time, will this deplete their battery back up, or, since we are only turning the power off, and not removing it completely, will this not kill the batteries. can anyone help?
Thanks
Brian Re

Ref, if you are taking away the primary source for the S7s then yes the battery backup will drain as it is used to retain the loaded program in memory.

but NOTE

Siemens and most brands have a timeline for replacing batteries...even under the worst conditions most batteries will last at least a year...in many cases 3 years.

You should learn this timeline then setup a program to replace as needed, if not before needed.

Since these stations are used for students, I don't see why retaining the program is that important. It's not as if your entire plant is depending on it. I'm in a similar situation and I've never worried about those batteries. If needed I replace them when I get a warning on the status LEDs. If I'm too late replacing the battery, then the student has to reload his/her program. If they don't have a backup on disk, then they haven't learned what I've been teaching them: to always make at least one backup on disk. BTW: the programs they are writing don't take long to load.

Kind regards,