Get 'better battery stats' from Google Play, and see what is going on. Does it charge to 100% and then reduce over time, or does it never reach 100% (ish) overnight?
The smarter battery circuitry will let it charge to 100% and then stop, and give the battery a rest before attempting to charge again (this is to preserve battery life, as overcharging is a real killer for lithium). It may be something wrong with this circuitry if it gets to 100% and then goes down. But down to 70 something percent doesn't sound right at all.
Also, what is the battery voltage when it's registering 100% (if it can get there) and when you take it off charge in the morning. (Disconnect and THEN look at voltage).