The Maxwell Liberty 2500 retrieves at 59' / minute with a 100 kg load. Assuming that it is drawing 40 amps for two minutes to retrieve 120' of rode and my 35 lb CQR, (what is that, about 14 kg?) you've drawn down a battery by about 1.3 amp hrs on a 100 amp hr battery.

liberty 2500 specs http://www.maxwellmarine.com/gen_liberty.php?dimensions

Even then, I doubt it would be drawing 40 amps. It's got a 50 amp breaker and it barely even breathes hard to retrieve the anchor.

In fact, the separate battery issue actually helped me out a few years ago, when my house bank was near the end of its life. As we came to the end of our four day cruise, there was not enough juice left in either battery bank to start the engine to enter the marina. So, we dropped the hook using the dedicated windlass battery and dug the generator out, ran it long enough to start the engines, then hoisted anchor and entered the marina. Sure, we could have done that all manually. But, it was nice that the windlass was still up and running.