Thomas sent us a question.

Hi there,

While I was reading your articles about batteries and mech vapes, a question came to mind – although it’s probably a stupid one.

To work out the value of the resistance coil I can vape with using a battery, I apply Ohm’s law.

But here’s the thing. This law links battery voltage level directly to battery amperage, so you can’t use a half-full battery with the same kit as a fully charged battery. It sounds logical, but I must have missed something, because applying Ohm’s law gives a strange result:

e.g. for a 3750mAh – 40 A battery in pulse mode and 25 A in MDC – 3.7 V nominal for a full 4.2 V

– Fully charged battery: 4.2 v / 25 A = 0.168 Ohm minimum

– Partially charged battery: 3.7 v / 25 A = 0.148 Ohm

– Almost empty battery: 3.3 v / 25 A = 0.132 Ohm

– etc.

Does this mean that the less charge the battery has, the better it will work with low Ohm assemblies? That doesn’t make sense. The only explanation is that the MDC must change as the battery charge does. I’d love to know!

Could you shed some light on my calculations?

Thanks to you and the whole team!

Dear Thomas,

Your calculations are correct! With a mech mod, the power sent to the assembly and the current drawn from the battery decrease as the battery loses its charge. So you need less power from it when its charge decreases. In fact, you would have to keep decreasing the resistance value to maintain the same vape power and draw the same current from the battery.

These three parameters work together, so if you lower the voltage, you also have to lower the resistance to maintain the current. However, the MCD of the battery doesn’t change, whatever the battery charge level is: it is constant. On the other hand, you need lower resistance to reach it when the voltage decreases.

These calculations only apply to unregulated mech mods. With an electronic box, the opposite is true. At constant power, we draw more on the battery when it’s almost empty. The resistance value makes no difference to the current being drawn from the batteries or to battery life in e-boxes, it’s only the power that matters.

Happy vaping!

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