A few months after purchasing my '09 Jazz 1.4 Ex, I was told by my employer that they wanted me to go to Malaysia to run their Office there for a year or so. Put car into storage and as part of the "mothballing" process removed the battery. Six years later, returned from Malaysia, went to get car out of storage and for fun connected the battery. To my great surprise all dash lights came on and there was enough power there to turn the car over a couple of times (failed to start, but not a battery problem). So, leaving your radio on for a couple of hours is highly unlikely to drain your battery!
Cheers,
Jock