I owned a cordless Black and Decker, the CMM1200 (24 volt, 19 inch). I have a 90x120 lot, a decent amount of that is yard, and I could mow about half of it with one charging. I usually could mow a little more, but would just do half the yard one night and the other half the next.
It would work great for smaller yards -- smaller than 90x120. It is manageable for a yard my size. For that particular model, any bigger and it may take another day. However, the new models are 36 volt, and look a lot snazzier, so you may have a lot better luck.
The one issue I had often was due to my laziness. I often waited quite a while between cuttings. This mower struggles to cut when the grass has been allowed to get too long. A gas mower will, too, but you just fill the tank back up. Something to keep in mind.
So, long rambling post summary: owned one, it was fine if you were patient and didn't mind keeping up on mowing, and honestly I would recommend it.