Question

Why does a voltmeter read negative?

Answer 1

Answer:

The voltmeter reads a negative value since the black lead is at a higher potential than the red lead

Explanation:

Answer 2

Answer:

If the poles of your voltmeter are correctly connected, there is a possibility that the battery suffered a phenomenon called "polarity reversal".

In this case there is the possibility that battery B will get a negative voltage. This can happen when there is a mixed use of old and new batteries together .

I hope it helps