Explanation

While my alternate power supply did work as it was suppose too, it shut itself off after 12.5 hours because of a low battery warning. Now, 12.5 hours is still impressive except when you look at what kind of battery I was running. For my test rig, as those who are active in the forum know, I used a 600W inverter and an Exide Commercial 8D-P1300 battery which is designed to deliver 450minutes of reserve time at 12 volts under a 25A constant load.

A borrowed amp-meter from a local car garage indicated a 37A draw by the inverter itself off of the battery while running the following equipment: 1) My box, 2) My 17" monitor, 3) My Cable Modem, 4) My 5 port hub, 5) My HP Deskjet 712C printer, 6) My Umax scanner, 7) 2 cordless phones, 8) A 12W Fluorescent lamp and my standard UPS which I kept in line just in case. While this setup power ALOT of equipment for 12 hours and that alone is impressive.

Now according to the math which I used earlier, this battery should have delivered 36 hours of run time at a 600W constant draw. This math was obviously wrong as so many of you flooded my email and tried pointing it out. And forgetting my math, the UPS is suppose to only deliver 450minutes at a 25A discharge rate. With all of the above devices plugged in, I was averaging a 40A load. 450 minutes is only 7.5 hours so why did I get 12hours out of it? Let alone the fact that I was pulling almost 1 and a half times it's rated load. At those ratings, I should have only gotten like 5 hours out of this unit instead of 7.5 or the 12 that I actually got. How is this explained? Well, batteries vary in manufacture and the rating of 450minutes reserve is probably a "safe" median between the best and the worst batteries out there in this same class.

Being that the inverter stayed at 37A most of the time, solid, and only went up to 42A while initially booting up the machine, I do not think this jump in run time can be explained by just simple chance or by a fluctuation in power consumption.