Is the best power cord no power cord at all?

Can anyone point me to a thread providing possible explanations as to why power cords can make such an important improvement in sound?

My friend is a tinkerer, and his theory is that reducing or eliminating RF is crucial for high fidelity, and that this is something that a well-constructed power cord can do. He says that Marigo power cords are designed to address RF, and there is no question that they have improved the sound of my amplifiers to a very material degree.

To take this idea one step further: My friend has also designed a preamp, a separate phono stage and a mod for the analog portion of an off-the-shelf cd player, each running on a separate DC power supply that has sufficient storage capacity to run these components with the power cord completely disconnected. Ie, stock power cords are hooked up to the batteries to charge the batteries when the system is not being played, but is then disconnected when the system is playing music. Playback time on battery power is in the range of 8-12 hours.

The batteries are large and expensive, but no more expensive than a high-grade power cord, which can be done without in this sort of system. And my system does play beautifully, with a noticeable improvement in the sound when the power cord is disconnected. His explanation, again, is the elimination of RF.

Any thoughts as to (i) whether reduction/elimination of RF is the source of improvement and (ii) whether this type of power-cord-less set-up could be incorporated into commercially available components?
Every noise source connected to the powergrid(from the generator to you house) contributes interference to whatever you plug into your wall socket. When running on battery power, these noise sources are eliminated, as well as the RF that an unshielded or improperly constructed cord will pick up(just like an antenna). That's also why power purifiers are so popular with persons able to recognize their benefit. It's more what IS NOT there, than anything that is added. With the noise/hash gone: everything is much more lucid and ambience information, that is otherwise masked, is more fully appreciated. This helps sound stage(depth and width) and imaging(or the picture on your HDTV). Of course- Those that can't hear it, or have systems that can't resolve it, will tell you you're nuts.
I forgot to mention: Most gear(those with outboard power supplies excepted) will have an AC power transformer within the chassis which will generate RF and/or vibrations/resonances as well. By utilizing pure DC: this potential interference source is also eliminated.
There are several high end battery powered products out there, including the battery option for the ASR Emitter amp and pre-amp, Sutherland phono stage, microzotl amp, Dodd pre-amp, battery option for Merlin S-BAM, and more that I am sure I missed.
The Lessloss DAC 2004 MkII, TRL Pre-1.5 preamp and TRL modified Sony NS900V CDP are other examples of battery powered components. Not to mention some turntable manufacturers such as Galibier Designs and Scheu use battery power supplies for their motor pods.

Some components do not require a charging period where the unit has to be shut down in order for the batteries to charge. My first battery powered component was an NEW DCA-33 amp which ran about 8 hours before it needed a charge. The battery box was massive and heavy. Today I can run my TRL Pre-1.5 and Lessloss DAC 2004 MkII all day and night and the batteries are housed in the chassis.

So not only can this type of design be incorporated into commercially available products the technology has advanced quite a bit. As to whether battery power is an effective means to reduce RFI and improve sound, as with any other type of power supply it is all in the design. Some will argue that a well designed traditional power supply will walk all over a battery power supply. I can certainly see their point of view as I can attest from the results I get from my amp.
how bout using ups for computer as battery powered. do we get less noise? rather than buying expensive power conditioner? is this be an option?