Well now that we've gotten this far, wouldn't you like to know how exactly I came up with saying that this small little battery will last thirty hours? Hard to believe isn't it? Well it's all in the math and before anyone jumps on my back about this being wrong... I've tested my equation and it works as it is supposed too. For those of you who are going to be angry at me for using math.... don't worry, it'll be really easy.

You need to obey the law of power conservation. Power = Voltage * Current.
The battery has 12V * 25A = 300W for 180 minutes.
The inverter, generating 300W (without any efficiency loss) would only run for 180 minutes (less if it was not 100% efficient).

However, the PC is not drawing the full 300W when running, maybe it's using 50W - 80W (without the monitor).
The total time would be 180 minutes * 0.9 (inverter loss) * 300W (output) / 80W (usage) = 750 minutes (12.5 hours).

That equation will work with any battery as long as you get the minutes reserve time and what discharge rate those minutes were counted at from the sales clerk. If he or she doesn't know and doesn't know where to find this information.... find another store to shop at. But, most of the time this information is printed directly on the battery label.

I really don't know what to tell you except to try this out for yourself! I'll try and get a second part to this article done sometime in the near future that'll tell you how to turn this into a real UPS so that it will automatically switch over when the lights go out. But until then, I'd buy a cheap $50 power strip with "5 minutes" of runtime and plug your system into that. Just keep this rig nearby and when the power goes out, your data will be saved by the cheapo UPS and all you have to do is unplug from the wall and plug into the inverter then flip a switch.

Then you'll be playing Quake III when everyone else is fumbling for their emergency supply of candles. And here's an idea.... this will of course work with anything electrical..... Playstation 2 anyone? [insert maniacal laughter here]