Why not batteries instead of power supplies?

I own the Veloce Lithio line stage, which is powered by lithium batteries;  it was a "hot" product a few years ago, and now is rarely mentioned or even on the radar. Vytas, the designer/manufacturer offered an update about a year or so ago which I recently took advantage of--one of the changes is the batteries- now much smaller than the big lithium green boxes that originally populated the unit. Despite this aspect of the design, the unit uses tubes- 6H30s, and I'm using NOS DR Reflecktors.
I have owned the unit for several years and have been very pleased with the sound. It replaced a Lamm L2 Reference line stage, which was also a very good unit. The Veloce lacks for nothing in the areas of bass or dynamics. It is also not noisy- to the contrary, using the Avantgarde Duo, a high efficiency  horn-type speaker with 104db sensitivity, the system is remarkably quiet. 

To add to the list, there are the folks at Definitive Audio/Living Voice in the UK that starting making full system battery supplies some years ago--covered in 6Moons, among other places. I'm sure improvements in battery technology have only helped them. Not sure if it is on their website, but they used to be set up in an Edwardian factory outside London. Long on my list for a visit. (Same folks who make those million dollar horns for your ship). They also sell stuff to lesser mortals, and seem to have a keen sense for interesting products.