So, I got my battery in the mail today and nothing has exploded yet. I'm impatient so I put it on the charger for about 30 minutes to get some testing in before going out.
The battery certainly makes an improvement,although it requires careful listening to notice. In comparing to the DI w/ isolator but no power supply, the Improvements seem to be 'sharper' sounding string instruments, 'blacker' background, and slightly more low level details and ultra low frequency bass (<30hz) likely as a side effect of the 'blacker' background.
In one of my main test songs, "Invisible Man in a Fluorescent Suit" by Shpongle, the opening 60 seconds has significantly more subtle details (especially the 'pat tat tat' sort of sound around 0:50-1:00) and the violin sounds more realistic like there is a quicker transition from one movement of the bow to the next. Around 1:59 there's some details in the background that used to be pushed back and required active listening that are now very clear. The drop at 2:29 and subsequent bass-intensive portions thereafter seem to reach deeper in the 20-30hz range.
Overall, it seems like a great upgrade that's worth getting over the power supply. I still can't really tell much of a difference using the power supply, such that it could just be a placebo. The battery is definitely an upgrade in sound quality, but I would say the USB Isolator and hex inverter swap are higher priority upgrades for the DI-V1. The difference in sq upgrade is somewhere between the isolator/hex inverter upgrades and upgrading the USB cable (I use a Furutech GT2).
By the way, regarding the whole switching between battery and usb thing I found it remarkably easy. Sometimes just flipping the switch works (especially if you're not playing anything), but if it doesn't these seem to have 100% success rate:
Switch from USB to Battery:
-Stop all playback on computer
-Unplug USB from DI
-Switch to battery
-Plug USB back in
Switch from battery to USB:
-Stop playback
-Unplug USB from DI
-Switch to USB
-Plug USB back in
edit:
P.S. No dropouts yet on battery, noticed some when switching to PSU.
edit2: changes seem more immediately noticeable on speakers -- very immersive soundstage and deep bass.