DIY Battery Monitor - ESP32 based

[Techstyle]

can confirm, the + sensor cable is only wire in the battery side of shunt. There is a resistor between the terminals but that's it.

I switched the cables other way round to test, but only thing changed was the amperage polarity.

It sounds to me like you have it on the Negative side of the battery?

This is a high-side device, your shunt should be connected to the Positive side of the battery, with Vin+ connected to the Battery side and Vin- connected to the load side (the side that goes to the panel.  nothing else should be connected to the battery side of the shunt, all cables (chargers and consumers) should be connected to the load side of the shunt.

Also, ensure you have removed the onboard shunt resistor from the INA219 board?