Looking at the DC data, it appears that it lasted for 6 days after the power went out. A day before it died, the battery voltage (Vbatt.dc) dropped below 12.8V. I would use this as a threshold to trigger the need for battery swaps.
In contrast, Vbatt.up and Vbatt.cc (the other solar-powered sites) have never dropped below 13.1. Thus, 2 racks of solar panels seem to be sufficient to keep a station running – albeit without much sensor heating.