I'll put my samsung galaxy s3 phone on the charger before i go to bed, and later throughout the night I'll get up and its fully charge to 100% but then after I take it off the charger it goes down to like 65% or lower, whats going on with it and what can i do to fix it?
I will give you some advice and hope they will fix your problem.
Is your charger right ? Your phone charger hole (data hole) may be broken (try to charge the phone with another charger). If the problem remains you should try to replace the battery with a new one. The problem may comes from your old battery.
If the problem still remains... you may need a service.