I have an off-grid solar setup consisting of four 100w solar panels, a Renogy Rover 20a charge controller, two 100ah 12v lifepo4 batteries wired in series, and a 24v 2000w pure sine inverter. The inverter powers a couple of cameras that draw about 20w constantly, and some heavier loads from time to time.

Before installing the shunt monitor, I made sure to charge the batteries to 100% (28.6V and no current flow from the charge controller). I then disconnected both the controller and the inverter from battery, calibrated the Drok and confirmed that it shows 0A when nothing is connected to battery. I set the battery capacity to 100ah and soc to 100%.

If I leave the system powered up for a full 24h with the 20w constant draw, the Drok SOC drops from 100% during the day (full sun for about 6-7h) to about 85% in the morning. When the panels start producing that morning, the charger does charge the batteries back to 28.6V, but the Drok never returns to 100% or anywhere close to that. It does show positive current going into battery while it’s charging. Over a couple of days of this cycle, batteries do return to 28.6V every day, but Drok continues to show less and less charge – down to 30%. At which point I reset the SOC and the cycle starts over again.

What am I missing here? Why is the Drok not returning to 100% when the batteries are fully recharged and do not take any more charge?