This is a terrible idea. I shall enumerate: • Lead acid batteries are 12.6 volts or so at full charge. You will not get there with a 12 volt power supply. You

This is a terrible idea. I shall enumerate: • Lead acid batteries are 12.6 volts or so at full charge. You will not get there with a 12 volt power supply. You charge a 12v lead acid battery at 14.2 volts or so. • The blocking diode he suggests will make this even worse, by a bit over a half volt. • He alludes to changing the computer power supply to something over 12 volts but doesn't say how. I promise: These is not a knob inside. You will reverse engineer the whole thing to figure it out and even then it may not be possible and you may be taking other components out of their safe design limits. • This scheme has no overcurrent protection for the power supply. A very low, large battery can take significantly more current than most PC power supplies will supply on the 12v rail. Maybe not for long, but long enough to cause a failure in the power supply.