In the theatrical cut, V’gers cloud in 82 AU in diameter. That’s like the orbit of Pluto. An AU is about 100 solar diameters, so it’s 8200 suns across. Assuming similar measurements in all three dimensions, that cloud is 700 billion times the size of the Sun, or about 900 quadrillion Earths, or 200,000,000,000,000,000,000,000,000,000,000 (we don’t even have names for numbers that vast) times the size of a Klingon battle cruiser.
Even in the DE, at 2AU across, that’s about 10 million Suns, 13 trillion Earths, or 3,000,000,000,000,000,000,000,000,000 Klingon battle cruisers.
I know these Klingons are supposed to be battle-thirsty warriors, but attacking something that large? Are you kidding me? All the firepower three battle cruisers — or the entire Klingon military for that matter — can muster wouldn’t have any impact on a target that size.