I use a Black and Decker battery powered string trimmer. I don't have a mower at this property, so I use it to mow about 1/2 acre. The battery lasts about 30 minutes and recharges quickly. Since I only "mow" in the evenings, after it goes dead I recharge it and resume mowing the following night. For that size area it is nightly exercise to keep up.

The reason I mow with the trimmer is I'm doing an experiment with tall grass. My city requires I mow to 12 inches. Before someone started complaining, my St Augustine grass was up to 32 inches tall in places. That seems to be the limit. Tall grass needs much less water. The roots are so deep that they can pull water from much deeper in the soil. I have an area of my lawn which has received only rainwater since October 2011. Since I live on the edge of the Texas desert in what appears to be continual drought, that is a long dry spell. That particular area is in full shade all day long. St Augustine is the only grass that will grow under that much shade. The tree above has a high canopy but not that high. The area gets only early morning sunlight and is in shade of the tree or house for the rest of the day. This year I watered one small area a couple times when I thought I could awaken the lawn early from winter dormancy. That did not work. The rest of the lawn has not been watered at all and looks great! Also I have not fertilized since Oct 2011. I expected the grass to become yellow, but it has not. Again, deeper roots bringing in nutrients from deeper in the soil.

Not electric, but I would look into the Stihl Kombi system and it's line of attachments. You can go from weedeater with string, to a weedeater with brush blade, hedge trimmers, edger, pole saw, leaf blower, the list goes on. I'm like you and have a lot of lawn and a lot of woods. I plan to purchase one later this year, just because I can have one piece of equipment with various attachments.