SKITTZO
Approximately 48 minutes.
The Devil
It depends on what is turned on without the engine running.
N2Audio
W/o being charged?
That is entirely dependent on what it s powering.
It has an ah rating of 35.
A system drawing an average of 35A (that s 1000w rms, roughly, at high volume) would probably operate for something close to, but less than an hour.
A standard head unit powering a couple small speakers -- probably ~10 times as long.