I bet your batteries PCB is being tripped. The link to the HV atomizers do not give the actually resistance, but even with a 5.2Ω atomizer at 6v your max drain is 1.15a, with a 4.5Ω atomizer your max drain at 6v is 1.33a. The max drain on the blue Tenergy 900mah batteries is <0.9a.
The max...