I have seen several implementations wherein the MCU is attached to BOTH an RTC with battery and to a serial EEPROM. The fast updates of "non-volatile" counters were put into the RTC RAM and then once per 10 minutes the values were also written to the EEPROM. The EEPROM update was also done when the embedded application entered and exited its time accumulate modes. In all the solution was fairly robust and kept there from being a need to worry about device wear-out.

Note that I did not implement that solution (I only prepared full design and flowchart activity for somebody else's medical device code) and would have probably used another technique myself.

Of course the most important consideration is if there needs to be 100% accumulation and storage. In many applications there is no great loss if the counter sometimes loses a few cycles under conditions of unexpected power down. If this is so then a simpler lower cost solution may be used. I worked on one application where the MCU was detecting external events and under unexpected power loss it was possible for the monitored machine to generate a few cycles that were undetected as the machine came to an orderly stop. So the count was "off" anyways in that case.

Michael Karas