Measuring the supply voltage of an ESP8266 should be a simple matter of calling ADC_MODE(ADC_VCC); then ESP.getVcc(). Would be too, if this board had left the ADC pin to float instead of connecting it to an LDR and a pullup resistor. "Wait, why is the voltage different now I've moved it across the table?" "Ah, the overhead light isn't shining on it any more". Doh!

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("received: topic","sensors/5CCF7F805547/voltage","message","3.07")
("received: topic","sensors/5CCF7F805547/temperature","message","16.00") ("received: topic","sensors/5CCF7F805547/humidity","message","42.00")

Now we're cooking with NiMH. Well, not literally cooking, I hope. 3 x fairly fresh AA cells gave a measured 3.8V at the battery terminals, but the LM1117 voltage regulator thing is eating 800mA. Have to see how long it lasts

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