It will shutdown without any negative side effects when the battery is empty after half a day or so. Don't forget to connect the it to the mains again when you come home.
Tip: in Control Panel>Power Options set the laptop to auto-hibernate after, say, 30 minutes of not using it. Then it turns off automatically if you leave it alone for 30 minutes.
Don't forget to turn this setting off (or switch to a power scheme that doesn't) when doing a lengthy Windows Update!
Hi,
First of all thanks for reading this through. Im having a pretty nasty situation here Im struggling with for days now. So lets get to it... I forgot to turn of my laptop so it still ran on battery and now Im on holiday for 2 weeks so Im pretty scared now that something bad might happen because of that. My laptop is pretty new and expensive. Could someone give me a better sight of this situation? Thanks in advance! 
Best regards,
Jonathan.
Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic