I don't think micro-pile refers to a specific device here that would have an exact EN equivalent. They're simply describing a phenomenon, not a device; they're referring to a source of very low voltage (a few millivolts) like a very small battery (and that's why they're putting it in quotes). I'd suggest microbattery if we were talking about minature devices, but it doesn't seem to be the case here. So I agree with your translation, which is a good description of this phenomenon.