I'm going to have to admit....I am not a Mac guy ...so others will need to answer this.Would it be possible to set OS X to shut the Mini down after x seconds/hours/days? I`m currently running OS9 on my pismo, so I can`t find out ;o)
A second battery would prevent your main battery from draining. However, the problem will be a reliable way to keep it charged. This is been debated to death under the power supply section of ths forum. There may be a way to do this, but it gets a little messy. I guess it depends on how much you want the Sleep functionality.How big of a problem will the current draw pose to a system with a second battery?