While I've Renogy panels and really like the company, I'm not familiar with this monitor. I've a Triminic that shows percentage of usable battery power (as well as voltage and current) based on the type of battery it's monitoring. That's what I go by and haven't paid attention to actual voltage. When it gets close to 70%, I start backing off using anything that will draw it down further - just being conservative.
I also installed my system so it only feeds one of the two 30 amp legs of my breaker panel, with the AC, electric parts of the water heater and refrig. on the other one. This way I won't accidentally run everything down to nothing.
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