I’ve seen this reported quite vaguely in some different forums but having experienced the problem a number of times myself I’ve now come up with the easiest solution. Basically once or twice a month my Nexus 4 running stock Android 5.0.1 eats through its battery in about 3 or 4 hours in spite of hardly being used. On the battery usage page it shows the culprit is the gmail application (I don’t actually use gmail but with Android 5 they have merged the email application into gmail).
Previously I would go to the applications page, click on gmail and clear all data, cache, stop the app and then have to reconfigure my accounts. I’ve noticed that simply force-stopping the app several times, then clearing the cache (which is usually very inflated – presently 100mb of data but 200mb of cache, and I’ve seen it as up to 800mb of cache usage before) seems to do the trick and bring battery usage down to normal.