I've done some quick power usage measurements for you.

At 12VDC the unit draws an average current of 503mA (6.036 watts). This was the average current measured over a 30min period with the unit playing. The filament heaters run whenever the player is running. The difference between no visual and the funnelweb visual is approximately 30mA, the visual seems to run even when not visible (select no visual to minimize current). But for a saving of 30mA it's not worth it. I was using line out to an amp, driving headphones will add a few mA but again not enough to worry about.

I don't know what size battery you were thinking of but a 12 volt 3.4 amp hour battery will give APPROXIMATELY 3.39 hours (3.4 * 0.5 / 0.503). The 0.5 is to allow for the fact that most SLA batteries are rated at the 20 hour rate, the empeg's cutout voltage and for a bit of headroom.

Also the player only turns the display off when it is in standby, the majority of the circuitry is still active ~225mA.

Rod.