Holy mother of necro threads!
Just kidding, of course, welcome to the TR Forums.
First of all, I wouldn't worry about the AC voltage in your house damaging your batteries. The charger usually does a good enough job filtering any spikes/dips in voltage to protect the laptop itself. In most cases of dangerously high voltage, the charger will go first as it is considerably cheaper to replace than the mobo on your laptop.
I can only speak from my experience here, but what I've noticed is that the slower you discharge the battery, the better it will keep its designed capacity. Likewise, if you quickly drain the battery by loading the laptop, it will deteriorate after significantly less cycles. Another thing I've noticed is that it is not detrimental to the battery to charge it before it completely drains or remove the charger before it's completely charged - this is because lithium cells don't suffer from "memory effect". What's more, if you don't discharge the battery all the way to 0% every time, you can significantly prolong its life. Some say that not charging it past 80% or so can do the same, but in my experience that's too much of a hassle to be convenient. I monitor my laptop batteries pretty much constantly and in the last year or so, neither one of the three I currently use has lost any significant charge capacity (or real runtime, for that matter) by following these routines.
So in summation: things to avoid subjecting your battery to:
1. High temperatures/direct sunlight (as it stresses the cells unnecessarily). This includes avoiding putting the laptop in bed or on a couch for extended period of time as it heats up.
2. Quick discharges. Use power saving mode, adjust your display brightness as low as you feel comfortable with according to surrounding light. Also avoid any applications that stress your system unless you really need to use them. You can monitor CPU load in Task Manager.
3. Draining it all the way to 0% every time. This is why Windows 7 hibernates at 7% remaining capacity and it cannot be set lower than 5% without registry hacks. I prefer not going under 20% if i don't need the juice urgently. However, a full discharge once in a while (monthly, for example) is recommended so that the electronics in your battery can adjust itself to the state of the cells (calibration).
4. Keeping it in the laptop if you don't plan to use it on battery for more than a month. This is not as bad as the other three, but it keeps it charged at 100% all the time and the laptop heats it up when under load.
5. Keeping the battery at 0% for long periods of time. This is absolutely prohibited as self-discharge of the cells can lower their voltage below a safe minimum under which these cells will not be charged by the electronics, in effect killing your battery.
EDIT: A helpful link I stumbled upon which explains in great detail what damages lithium cells: http://batteryuniversity.com/learn/arti ... _batteries