Compact 12V Battery Monitor Circuit

I need a small, ultra-low-quiescent-current board that keeps an eye on a 4-cell, 12 V NFPP sodium-ion starter battery and tells my Garmin G3X Touch when something is wrong. The core job is purely analog—no firmware, no high-current switching, no BMS functions—just reliable threshold detection with clean signalling.

Functional brief
• Trip low whenever pack voltage falls below 11.0 V.
• Trip high whenever it rises above 15.8 V.
• Add a simple temperature probe so I can alarm on extreme pack temp later (bring the sensor onto the PCB and break it out; the actual temp limits can remain adjustable by resistor change).
• Expose one protected, open-drain fault line that the G3X Touch discrete input can read (search “Garmin G3X Touch discrete input EarthX battery” for reference behaviour). This can be a wire.
• Filter cranking noise and other fast transients so the line stays quiet during engine start; a few hundred-millisecond qualifying delay is fine.
• Operate from the pack itself, drawing as little current as practical—tens of µA at most when idle.

What you’ll hand over
1. Schematic with clearly marked thresholds, hysteresis network and temp sense section.
2. PCB layout files plus Gerbers/ODB (KiCad or Altium preferred, let me know which).
3. Complete, order-ready BOM with manufacturer part numbers.
4. Two prototype boards assembled and shipped to me.
5. Bench-test report showing trigger points, propagation delay, output behaviour into a 5 V pull-up, and start-up transient immunity (scope screenshots or logic-analyser captures are perfect).

Acceptance
The prototypes must trip within ±100 mV of the stated voltage thresholds at 25 °C, consume