Motorola has a device that is powered by stomach acid. Given that a battery consumes the electrolyte as it generates a charge, how much power could be generated using a device such as this? Let's assume the electrodes are large enough that the electrolyte is the limiting factor in this reaction. Would the body just generate more acid to compensate? Would there be any physiological side-effects from using such a battery?

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    $\begingroup$ Sounds like one for Randall from xkcd $\endgroup$ – sehe Nov 29 '13 at 22:02
  • $\begingroup$ The acid isn't the relevant consumable, the electrode is. $\endgroup$ – Aesin Nov 29 '13 at 23:55
  • $\begingroup$ @sehe I was thinking the same thing, although this one may not have enough physic for him. $\endgroup$ – bobthechemist Nov 30 '13 at 2:13
  • $\begingroup$ @Aesin In my understanding both the electrodes and the acid are consumed. Let's assume we have large enough electrodes so that the acid is the limiting factor. $\endgroup$ – Mr. Shiny and New 安宇 Dec 2 '13 at 14:04

Well a battery works on the principle of dissolving one of the electrodes with the electrolyte. This means that you would have a solution of the metal and electrolyte in your stomach. If consumed in large quantities or in quick succession, then you most probably would notice some physiological effects, however, I would assume they'd be very minor given the mass of the tablet in question. Other than under those circumstances, I would expect the physiological effect to be non-existant. Given this has been approved by the FDA, you can be pretty confident that it's safe.

  • $\begingroup$ Thanks, but I was wondering more about the case where the electrodes are large enough that the stomach acid is the limiting factor in the chemical equation, not the tiny microchip-sized battery that Moto is making. $\endgroup$ – Mr. Shiny and New 安宇 Jan 20 '14 at 14:10

The electricity generate depends mainly from the electrodes. This is the same misconception of lemons battery. In fact the energy of every battery comes from the metals and not from the acid use as electrolyte, as you can't generate energy from lemon juice but from the different potential between copper and zinc coin so you can't generate energy from a stomach acid but with it. However $HCl$ is not used normally for battery so I think you could not produce a big amount of energy even if you ingest very big electrodes.

  • $\begingroup$ I know that the energy doesn't come from the acid. However it stands to reason that if you have only a tiny amount of acid relative to the size of the electrodes you won't have a very good battery. $\endgroup$ – Mr. Shiny and New 安宇 Jan 20 '14 at 14:12
  • $\begingroup$ @Mr.ShinyandNew安宇 yes you are right so It will depend on what you have eat at breakfast and how you are digesting it! Nice strange question! $\endgroup$ – G M Jan 20 '14 at 14:16

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