That's bit unusual. My MBP looses less than 2% overnight (well, depends how long the night is) while sleeping. Now, every battery will loose few % from 100% when not in use - and 0.5-2% is probably at or below battery sensors ability to measure anyway. But have you left computer powered off for longer time, is it loosing power further? I would not expect it to loose much beyond few % and then level off - when powered off.
Power draw while sleeping depends on which device you have (higher end MBP needs more power - larger RAM to keep powered), but I never lost more than 5% in 24 hours while sleeping and that is negligible value in my use.