At 2:53 in the video when he shows the inside of the box, it looks like the batteries are stacked; the spring on the right is at the top and the spring on the left is at the bottom; so looks like the negative of one battery connects to the positive of the other.
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Found a specs sheet that describes it as dual parallel, (not stacked)
http://bamavapor.com/ATB-Kamagong-TI-Chip-Box-Mod-99101610/
Specs:
- Made in the Philippines
- Manufactured by Pinoy Wood
- Dual parallel 18650 batteries compatible
- TI Chip
- A variable voltage wooden box mod that uses a Texas Instrument regulator chip inside it
- Performs superbly well as the switch can go up to 10A of current
- Body made from Kamagong wood
- It can fire lower ohms coil, minimum at 0.6 ohms
- Power up to 60 watts maximum at 6 volts
- Triple the current of a ProVari switch
- No cut off point or E1, E2, E3, E4 errors
- Dual batteries, last you 4 days per charge
- Limited lifetime warranty through the manufacturer
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Found a good picture that clearly shows two springs at the bottom for a dual parallel arrangement:

(This picture came with a "DNA30 caption")
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Then there's this other picture which looks like the model shown in the video: this one shows the springs I saw in the video and this setup looks like stacked batteries.

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