I just PMed you before I saw this new thread. But I'll post my opinion for everyone else's amusement!
I used Optima Red Top car battery with Deltran Battery Tender charger when I was using Altmann BYOB amp and Altmann Attraction DAC, both were battery powered. It worked great. The amp had plenty of current for impressive transients on my Legacy speakers, but it only made 10W into 4 ohms at clipping, so it didn't last long. But the battery system was excellent. I liked the freedom from hum, PCs, I liked playing music in the summer lightning storms every night in late spring. The car size battery lasted a long time without charging. The Battery Tender can be left on all the time and not hurt the battery, it is intended for long term storage of vehicles. It has extremely low trickle, and smart logic to charge up to 1.5A when necessary. It knows what the battery needs and automatically provides it. I still have my Battery Tender and I think about going back to all battery system again. My chip amps need +/-24VDC so I'd need 4 batteries and chargers. I could not hear the difference with charger on or off.
The red top battery is very low impedance, much lower than typical plate batteries, and quieter. It has comparable performance to a aftermarket audio regulator like Belleson or Hynes. It is sealed, can be installed upside down, no risk of leak, safe for indoor use, imo.
Since the tube preamps are class A, the current draw from any power supply will be steady, so the PS will see no music transients. So anything rated adequate current should work fine. Remember, there is a distinctly non-audiophile DC-DC step up converter inside the preamp, so don't get too crazy over the quality of 12V you are providing. You don't need upgrade power cords on the 12V supply. The PS never sees music transients because the preamp is constant current draw class A.
Your price estimates are way too high, imo. Maybe that's Long Island pricing?
You can buy a 12V 6.8A frame power supply from mouser for $103. See your PM for link. Box, fuse, switch, cables should bring to $200, +$100 labor. Make sure 6.8A is enough current. A battery can deliver much more than that. If it were very efficient step up converter it should be enough, but check to be sure. If it only needs 1A then there are less expensive supplies available.
Red Top battery is at any Advance Auto for about $150-200. Battery Tender is $45 from Amazon. You hook it up, no labor.
