I dont use mine for long periods at a time, mostly for checking connections when I am soldering cables or making a new pickup, for about 5-10 mins at a time, and doing so a few times per week, I have the original 9v battery in it for over 18 months now, so I'd guesstimate that you might be able to get about 8-10 hrs on a 9v with the volume at 50% and gain about 10%.
The louder you play it, the faster it drains the battery.
Also, I've run it on a 9v powersupply too, the OneSpot and it is a little louder when doing so because the OneSpot offers a higher current than a 9v battery. Remember, amps x volts = watts.
Also, keep in mind that the tiny speaker and the LM386N op-amp circuit that is inside is not going to win any awards for audio fidelity and the electronics inside seem to be based upon an amp design from the 1940s. As such, compared to even a small practice amp, such as a Fender Rumbler bass amp (~$70), with a uke plugged in, the Honeytone sounds like a toy or much like an AM radio compared to basically ANYTHING else. IMHO, it is more novelty than a musical item.