The first battery powered preamp, the Mission 776, used two 12 volt lead-acid in series. Those type of batteries are still used in emergency lighting and are not expensive. Dynamics was not an issue. I only had to replace the batteries once in 6 years. Much of the cost is in a reliable, automatic charging system. On the other hand, the batteries in laptop computers can be very expensive to replace.
Tubes require high voltage which means many batteries, probably smaller, in series.
Tubes require high voltage which means many batteries, probably smaller, in series.