The ART USB Phono Plus can be used on battery power, but the USB power needs to be blocked because the Phono Plus can also get power through the USB port from the computer. The back of the Phono Plus says it needs 9V DC. AA batteries are 1.5V, so 6 of them is 9V.
I used a power blocker from Amazon. This blocks power from the computer getting to the Phono Plus, but allows data transfer.
Use a battery holder to hold 6x AA Batteries. This battery holder from Amazon has a pigtail that plugs into the Phono Plus, plus it has a ON/OFF switch. With 2000mAh batteries and the listed 150mAh current draw listed on the back of the Phono Plus, you should get 10+ hours of use with a full charge. Which should be more than enough for a days session of recording. I bought some EBL rechargable batteries (2800mAh) for $12 for 8 batteries.
I then put some double sided foam tape between the battery case and the ART USB Phono Plus to combine them as one piece and put some feet on the access door of the battery case. Now it is a fully self contained and self powered unit, with the batteries accessible from the bottom.
How To: ART USB Phono Plus On Battery Power
Re: How To: ART USB Phono Plus On Battery Power
After accidently leaving the system on several times, I can confidently say the batteries shown above will give about 30 hours of runtime before needing a charge