Is voltage measurement of a battery done in series?
This situation is a something of a paradox, yes, but you need to understand that 'series' does not mean 'not parallel', and vice versa.


Any components which form a loop in which current is allowed to flow are in series.
Any loops which share the same potential difference across them are in parallel.


In your example, current flows from the one battery terminal to the other through the voltmeter, which acts like a very large resistance (10M-50M, typically). Current is flowing in a loop, therefore the two components are in series with each other. The voltage across the battery terminals is equal to the voltage across the voltmeter, therefore the two components are also in parallel with each other.