More apps pinned doesn't pinned to the start screen does not mean more battery drain. Since you are running Windows Phone 8, there is an extra ability that pinned apps get:
If the Tile for your app is pinned to the phone’s Start screen, the
expiration time for your background agent schedule is automatically
extended to two weeks whenever your background agent calls to update the Tile.
In otherwords, as long as apps that are pinned behave, their background tasks do not get cancelled after two weeks of inactivity like other apps in your all apps menu.
But these apps get at most 25 seconds every 20-40 minutes. This would NOT cause a large battery drain. Also these apps still have to behave and fall within a bunch of other guidelines in order to keep running in the background.
Microsoft has gone to great lengths to give developers the tools they need to give users apps they want to use, but at the same time, prevent abuse that would cause a bad user experience.