I went for a flight today with 4 batteries and ST10+ fully charged. I flew for around 18 mins with battery 1and got the low voltage warning, so I landed the drone and changed the battery. Everything was normal at this moment, there was 12.5v in battery 2 as displayed in the ST10+. But when I started flying with the battery 2, the voltage keeps changing until it reaches 10.6v and forced me to land. I've double checked that everything was fully charged and also tried flying with battery 3 and 4 but it's still the same. Anyone got this problem?