Theoretically, yes. Apps running at background do consume memory (their threads still exist and that's why you can see them listed when you double click the Home button), and thus they do consume battery.
But practically, not really. iOS does a fairly good job on memory management, and apps running at background only consume a small amount of memory. And if other apps running at foreground (actively running and users are interacting with them) need more memory, the iOS system may terminate the background apps and purge the memory. The reason that sometimes force-closing an app seems to save memory/battery life is because that, some apps may request to run long-running tasks even running at background, for the purpose of, for instance, background fetching, periodically syncing data, etc (note that not every app does that). But you can disable these by configuring Background App Refresh in Settings -> General.
So in summary, for an app that isn't doing much when at background, force closing it won't yield noticeable benefits.