Results vary probably on settings, model, temperature, battery brand, etc. But the number I hear from Vox and other users is 15-18 hours. Which, in my book, is freaking incredible. Keep in mind that this is two AAA batteries, not four, so it's pretty inexpensive.Can I ask, what's the battery life like with the Amplug? I really hate buying batteries. That's one thing that makes the phone and app option seem more attractive.
If you're using the cheaper IRig interface I'm not surprised. The good interface is $90+ and has high quality audio.I prefer the Vox AmPlug over the iRig. For some reason the iRig sounds like crap to me. Although my best (not-very-portable) headphone setup is probably the Fender Mustang I amp.