How old is the battery? I'll assume the charging system is OK, being you've gone to work and that means running down the battery getting there, but the charging is not the case. Have to get a voltmeter and note how much the battery drops from its static 12v.
With the meter set to 20v, see how much the battery shows now? Say it's 12.4v. Now start the bike. If it drops under 10v read at the meter, it's a bad battery.