the battery was on a full charge.
Are you *sure*? Doesn't sound like it to me given...
the "full" light was never on except when the v3 was turned off. I soon as I would turn the v3 on the light would dinm.
If it was full, I would expect it to register as such even with the V3 plugged in. Now...I don't have one of these, but I have a damn near similar batt quite possibly made by the same manufacturer that I use with my T+ UA5.
how fast do the lights on the battery go down?
Depends on the draw, of course. Even with power-sucking mics, the V3 oughta only draw around 1,000 mA. I can't answer how fast the lights should go down because I don't use the exact same batt with my V3, and I don't know how the lights are calibrated internally in the batt. But...it seems like you lost juice quickly given...
after about 2 and a half to 3 hours I was at the last light on the battery. it never died but I got a bit worried b/c I have read that they will go for up to 6 hours.
If it's a 5400 mAH battery, it should run for roughly 5 hours - and 2.5 - 3 before the last light seems mighty early.
I know it doesn't matter but the v3 low battery light never came on.
True, the V3 low batt light won't come on unless you recalibrate it. Instructions in the Archive or on the Grace website if you wish to do it.
doesn't seem right to me for it to be on the last light at only close to 3 hours.
Me, either. Only thing I can figure is either [1] it wasn't a full charge, [2] it's a faulty batt, [3] there's a problem with the batt > V3 cable /connector wiring causing it to draw far more than it should, or [4] it needs cycling to achieve it's full potential (supposedly LiIOn batts are immune from needing to do this, but IME I've found otherwise.