I have a NASA BM-1 battery monitor that I fitted about 12 years ago. I couldn’t be without it. The important thing is to know how many amps are being charged, or discharged at any given time. Indicators of the level of charge are a bit subjective depending on the algorythm used by the monitor manufacturer and the battery type
I now have a LIFePo4 house battery with bluetooth and using an app on my phone I can determine the state of charge of the battery, but the app does not tell me the rate of charge or discharge. I have contacted NASA to ask them if they intend to bring out a LiFePo4 compatible monitor and they replied saying they had no current plans to do so.