how to log and graph battery (cell) voltage over time?

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baltika_no_9 pid='19430' dateline='1620849942']

The Pi is on my boat in Greece and data is updated every second but, in addition, the data is sent every 10 minutes over the internet to my home in the UK where the battery measurements are stored in an InfluxDB database. A Grafana graph (see attached example) plots the data.

I'm interested in this- how did you do the  telemetry part?

On the boat there is an ADS1115 to measure voltages which is connected directly to a NodeMCU/ESP8266 running ESPEASY
ESPEASY sends data (1 reading per second) over the boat network as UDP to my Node-Red Dashboard / SignalK on the Openplotter RPi
In addition, the ESP8266 also publishes the data (1 reading every 10 minutes) over the Internet using MQTT to the Hive public MQTT broker.
I have a Home RPi which subscribes to my Topic on the Hive MQTT broker and pulls the data sent from the boat into another (Home) SignalK server
I run the SK InfluxDB plugin to record the incomming data and plot it using Grafana

When the boat is laid up over winter I can turn the Openplotter RPi off and leave the ESP8266 sending only the 10 minute MQTT messages.
It worked well last winter - I havent been to my boat since last September but I can tell you that the house battery is at 12.7v right now.  


Hope this helps

Please forgive me if I'm being obtuse but I'm not clear on how the process is working. The EPS8266 has a single WiFi capability if I understand it correctly. The frequent (1 second) updates require the ESP8266 to be associated with your on-board WiFi network but the less frequent MQTT messages require it to be connected to a public WiFi thus giving Internet connectivity or is that Internet link achieved by some other method?

Thanks

Hi
The attached diagram shows the layout of my boat network and the ESPEASY Wiki may help explain a bit better than I can here

My ESP8266's have one WiFi connection to my LTE Router but the ESPEASY firmware allows you to specify up to 3 "Controllers"
When on the water, my first Controller is configured to send and receive UDP packets to my OpenPlotter RPi every second. 
This is sent over the local WiFi network with no Internet connection required
The second Controller is my MQTT controller and is used to send data over the Internet 

Within the ESPEASY firmware there is a "Rules Engine". 
The rules engine allows me to run some simple code which tells ESPEASY to read the battery voltage sensors (ADS1115) every 10 minutes and Publish the data to the MQTT controller. 
This DOES require an Internet connection so, when in the yard, my LTE router is permanently connected to the Internet but only used to send this small "burst" of data every 10 minutes so LTE modem data usage is very small

(When in the yard, the UDP controller is switched off)