Posting a picture of your battery usage would provide more insight into your problem. Android system will ALWAYS run in the background on your phone, and will be one of your largest battery drainers if you don't use your phone much. Excessive battery drain could be symptomatic of installed apps that are set to sync too frequently, a bad battery, etc. If you're running a custom Rom on your device, there could be issues there. If you don't know what a custom Rom is, don't worry, you're stock.