I have a SmartSolar Charger MPPT 100/30 on a boat with an alternator that does not have an external regulator. I'm seeing an issue where, when the batteries are fully charged, the solar controller is on and in float, and the engine is on, I'm seeing voltages between 15.25 - 15.45. That is definitely too high. The solar controller reports it is in float and putting no amps into the batteries, but when I turn it off, the voltage drops to 14.8, which is closer to normal. Why is the Solar Controller increasing the voltage in this situation, and is there anything I can do other than turn it off when I'm underway?