If your phone uses your Live account and you also added an Outlook.com e-mail account to the e-mail settings, it will read contact information twice.
I had this problem as it showed me dupe contacts, calendar events, and tasks. Now multiply that if you also have Skype, LinkedIn, Twitter, and Facebook linked to your Outlook contacts account. I set up the Outlook account because it was an option in Office... bad, very bad. They've eliminated the ability to do that with WP 8.1.
To fix this on your phone, start by making sure you don't have a separate Outlook e-mail account listed. Now, select a contact you have listed multiple times. Tap the middle button at the bottom of the screen (between Pin and Edit) and select other contact records that are duplicate records for this contact. Don't worry. Unless there's a conflict, all the fields will be merged, so if you have an address in one but not another, they will all show under the merged listing.
To fix this in Outlook (if you have FB, Skype, LinkedIn, Twitter connected to Outlook), go to Outlook.com on your computer and select the People app. Tap/click the name of a person for which you have multiple records, then tap/click the Links item on the menu bar and associate all those records with the same person.
I doubt if this is the source of the battery drain. In the syncing process, the phone will send a timestamp to Outlook.com to see if one or the other has more recent information. If they're the same, no further communication occurs.
If you're running 8.0, you might go to Settings, then swipe right to Applications. Here you can check for apps that are running in the background. Turn off any that only need to be updated when you use them (i.e., banking apps) and clear the option to start running in background when you use them (why undo all that hard work?)
If you have 8.1, the Battery Saver app can tell you which apps are power hogs. Tapping on an app name allows you to turn off background.