Very confused why my battery shows a low voltage but soc shows 100% until a load is put on then jumps to 13.6 and about 10 min later drops back down to 13.1, and will jump back up when I turn on the fan in my camper which is 30 watts. I checked the battery terminals with a multimeter and reads the same. Epever 4125, lion energy battery. This all started happening after I disconnected the battery to change a USB port in the camper. Any help would be greatly appreciated