I have or had quite a few DNA mods powered with a FullyMax 900 mah battery. Keep in mind that it has the same capacity as a 30 amp 2700 mah 18650. I have my doubts as to try to fit in a larger battery.
What wattage are you using it at ?
Have a look at this thread:
https://forum.evolvapor.com/topic/72119-dna-100c-wattage-drop-after-3-puffs-geekvape-z100c-p-coils/#comment-940230
The situation where you have 3.2 volts between output and ground is troubling.
This is something that I have no experience with so I measured the voltage between output and ground on two of my DNA60s and my one DNA60C, all three read about the same, just over 0.7 volts.
And no change if fire button pressed.
A lot of computers with USB 3 ports still have a USB 2.0 port as well. Did you try plugging into a different USB port?
I should delete this as it's a USB-C board but will leave it. Please disregard above.