The battery only charges while on power, and when it is needed. In other words, if you unhook from A/C, then plug back in, the battery will be charged, and not charged any further.
Most batteries will only last 2 maybe 3 hours, unless you have a SSD drive installed, then you may get around 6. I can get 18 hours out of my netbook with the SSD drive in it. If I need to charge it, I can take it out to our van and plug into the a/c plug in it.
My Toshiba will not run without a battery in it---charged or not.
Newer batteries do not have the memory issues old ones did. Manufacturers do still recommend you fully charge a battery the first time before using the device---laptop, cell phone, etc. I guess as a creature of habit, I fully drain my laptop battery now and then. Two hours or so is what it delivers and did when I got it.
The little netbook and tablet things are incredible, in comparison, as far as battery life. As mentioned, even with wireless internet, the towers will probably go dead if power to your area is out.