First cut the battery bank in parallel so you get more capacity and a lower discharge rate. Put a small DC‑DC converter that pulls from the bank when the panel voltage drops below a set point. Add a diode to keep the flow one way and a manual bypass switch so you can cut the panel if it blows. If the battery reaches a critical low, have a tiny wind turbine or backup panel wired in parallel – it’ll pick up the slack. Finally, log the voltage in real time; a simple microcontroller can trigger an alarm or switch to the backup before the main fails. No fancy gadgets, just a reliable parallel battery setup with a hard‑wired cut‑over.

Good point on the hysteresis – no need for the converter to jump in and out at a single point. A simple ±0.5 V band will smooth things out. The thermistor idea is solid; batteries choke up when the temperature drops, so catching that early is better than letting the bank hit the low‑voltage cutoff. Locking the bypass switch when the system is autonomous keeps human error out of the loop. Add a small relay that only engages the bypass if the temperature sensor reads below a set value or if the panel’s voltage stays below threshold for a few minutes. That gives you a layered fail‑safe that’s both mechanical and data‑driven.