Why not batteries instead of power supplies?

There are lots of reasons to avoid the house AC if at all possible. Aside from voltage regulation there's also the issue of RFI/EMI coming in along with the voltage and current, the cost of power cords, the high cost of a good power supply especially for high power amps, ground issues, fuse issues, transformer issues (magnetic field and vibration) and the need for huge capacitors.

@geoffkait

I knew that AC could be a problem. Is there a way to hook up an amplifier to a battery pack and avoid AC altogether?

A few years back a company was showing a strong presence at RMAF that had a few components that were 100% stored DC power. Although they didn’t sound extraordinarily good, the idea was launched. For some reason it never caught on, but doesn’t PS Audio already somewhat address this with their Regenerator P5 & P10?

The negative side of battery power supplies is the supplies themselves have inherently high output impedance compared to their AC counterparts, leading to higher cross-talk, and potentially weak bass and dynamic range.

This is all theory, of course, as is the benefits of battery supplies. I’m just playing devils advocate. It's not a 100% free lunch, and has its own set of challenges.