I have done this for years. I currently (no pun intended) have two such setups operating. Hooking up batteries is no more dangerous than jump-starting a car,

I have done this for years. I currently (no pun intended) have two such setups operating. Hooking up batteries is no more dangerous than jump-starting a car, and we are all adults here -- just think things through carefully. Car batteries, or if you want to go even cheaper, the "lawn and garden" riding mower batteries from Walmart, are not made for repeated deep discharge, as some other alarmist posts in this thread have pointed out. However, you start your car several times a day, but the power goes out much less frequently, and every power outage doesn't run it all the way down (if so, the UPS isn't helping much). A few additional points: 1) The wires that attach to the battery should be big. Canabalized lamp cord or such will not work; worse, it will appear to work, until the compture runs off the battery for an extended amount of time, and then it can get hot enough that the plastic gets bubbly and then bursts into flame. (Not my personal experience, I use super heavy wire from old well pump wiring, that is about the size of the leads to a starter motor on a car -- about 12 or 4 gauge). 2) If a cheap UPS says it will keep the computer up for 15 min, it is likely not cooled enugh to run continously for hours without burning out. Look at refurbished computer places, or Goodwill Computer Works in Austin, and get the APC brand UPSs or similar, and look for those that have fan to actively cool them when they run on battery. 3) For reasons 1) and 2) above, TEST THE THING outdoors, giving it a full change and then putting several 100 watt lamps on it and letting it run down. 4) I put the entire thing in one fo those big plastic tubs, that looks like a big tuperware container, to keep acid from the non-sealed battery from ever getting on the floor. I leave the lid on loosely, so the power cords can get in and so hydrogen gas can not accumulate. Another thing, is you can put jumper cable style clamps on the battery wires of the UPS, not close it up, and use it to make AC current for running saws and such where there is no electricity. If you do this wtih cheap UPSs from garage sales, you will swiftly find that you can light the cheap brands on fire, and that APC rocks. A battery that may not be good enough to start your car on cold mornings may keep your computer up through occasional 3 min outages for several years.