Note there are a number of battery-powered solid-state phono stages. The Boozhound and the Hagerman Bugle come to mind. Then there's the Oatley K301 that uses a 6418 "pencil" tube first/gain stage with a solid state buffer stage (wired like a cathode follower, can't recall it's name). While the K301 uses a mains supply, B+ appears to be 30v so you might be able to power it with batteries. Filament is 1.25v at 10mA, but it looks like it's pulled off of the B+ somehow so I'm not sure what the total draw is on B+. Note the filament supply seems odd to me, but a lot of people like this phono pre.
Finally, if you like to DIY from scratch, Steve Bench has a 6088 "pencil tube" phono stage that he powered from batteries. Life is about 200 hrs on D cell filament batteries and B+ is apparently 2mA at 70v. It uses 8x 9v batteries, and if we assume they are 200mAH batteries, we'd get 100 hours out of them (in theory).
OK, just a few options. I think I may have posted about some of these in an earlier post several years ago, but I can't recall.