S4C+ M2000 problems after power down

A S4C+ controller that has been running well for more then a year after commisioning now, is now giving frequently problems after power down, power up.
A year a ago the SMB battery an the battery beneath the computer in the controller cabinet have been renewed.
Custumer says the problem is resolved by restoring backup of the program.
You should suspect the computer battery, but the customer says there are no specific messages about the battery on the teachpendant.
Can I measure the status of the computer battery electrically? If so, on which connectors can I measure what voltage?
Could there be a problem with the flash ram that stores the image after a power down? Where can I find the flash ram, and how can I diagnose it?
Or could it be the main computer?
Would making a cold restart and reïnstalling the system be a good idea, although the systems seems to start now without problems, only the program seems te be corrupted after power down?

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