> But the controller+inverter should be running if supplied with voltage from solar/wind/generator regardless of how the batteries are doing.
Most of them don't operate that way. They need the battery bank connected first, and run off the battery bank side, while controlling the panel side.
Some may tolerate that sort of recovery from deep discharge, but it's not a safe bet, and some controllers are pretty clear that if you connect the input side before the batteries, you'll damage the controller.
A dumb PWM controller stands a better chance of doing this, but something like an MPPT controller, unless it's explicitly designed to fail into a PWM configuration at low battery voltage, won't - they need power to drive the buck converter circuitry (the controlling ICs and oscillators and such) in order to get power out of the panels.
Most of them don't operate that way. They need the battery bank connected first, and run off the battery bank side, while controlling the panel side.
Some may tolerate that sort of recovery from deep discharge, but it's not a safe bet, and some controllers are pretty clear that if you connect the input side before the batteries, you'll damage the controller.
A dumb PWM controller stands a better chance of doing this, but something like an MPPT controller, unless it's explicitly designed to fail into a PWM configuration at low battery voltage, won't - they need power to drive the buck converter circuitry (the controlling ICs and oscillators and such) in order to get power out of the panels.