I have a SmartSolar MPPT 100/50 connected to 420W solar panels and two 300Ah LFP batteries in parallel (12V system). It charges during daytime to 100% SOC/14.3V. But when there is zero load on the batteries, the SOC always trickles down to 87%/13.3V by morning. I charged the batteries to 100%/14.3V and disconnected the charge controller, and they hold their charge all night no problem. Why does the charge controller drain power off the batteries by 13% every night, despite there being no other load on the batteries?