Hmm yeah, I wonder if there is any reasonable solution to this. One common way to easily set RTC of USB devices is to monitor timestamp on files written to USB drive. Then just sync the time right after the write.
Also if I added proper power saving support to the Pawn runtime, it could possibly be left on for a long time. Most power-consuming parts of the system (ADC, FPGA, switching regulator) can be switched off and MCU could go into standby. The standby current consumption should be less than 1mA, giving a few weeks of standby time.
Too bad that they didn’t make use of the RTC in the microcontroller. Would have required just two diodes (to drop 4.2V → less than 3.6V) if one is happy with LSI oscillator accuracy (can calibrate it right before sleep).