Needed more power for my networking equipment
 

And of course, I like to keep the budget tight. So I found a 22 dollar lawn/garden (tractor) battery at o'reilly. I bought it originally for starting the generator when the stock battery failed and so did the pull-start. I ended up keeping it though because I knew I could use it for this.

I took the old gel-cell out and made up a cable from an AC power cord to plug into the battery cable internally. Once that was done, I put donut terminals on the other end, then drilled the battery terminals to accept a screw, and screwed the donuts on. I tested the voltage running, then on drain to make sure it would be compatible, then cut a cat litter bucket to set it in, in case of an acid leak.

The equipment, consisting of a cable modem, a cisco 1841 router, a dell gigabit switch and a netgear wireless router all pull about 55 watts total per the kill-a-watt meter a friend has let me borrow. So far it has run those devices for about 20 minutes during a power outage, so who knows how long it will go over time. I don't know yet what voltage the UPS kicks into high alert for, but if it's around 11v, then I might have a couple of hours of run time :D

Pics.

All set up:
http://texasoverclockers.com/modules...10002/ups1.jpg

Running voltage:
http://texasoverclockers.com/modules...10002/ups2.jpg

I wouldn't use a larger battery for such a small UPS because of charge load, but on a larger one that uses 24v (2x12v gel-cells) I might be ok with 2 slightly larger automotive batteries. Not sure how far one can push these, but there's been alot of buzz on the web over this so I don't feel too concerned over the 55w load I put on this one (APC Back-UPS CS 500).

Here's an excellent article on the subject from good ol' Dan

The DIY (or, if you must, "Ghetto") UPS

Upgrade your UPS! (with some car batteries...)