Hi @giowild, according to the nRF51822 product specification, the trusted power source should range from 1.8v to 3.6v. The spec does not present the stop-working voltage. If you power it using 1.5v power source, it might work, but not stable. I think that is the reason why the spec not documenting this characteristic. So there is lot of unpredictable things if you power the Nano beyond the recommended voltage range.