I have samsung galaxy s. my battery drains out in morning completely even I had slept for just 4 hours.?

Battery was fully charged. Strange fact is, it works fine during the day. But I guess battery drains out when phone is idle. I have wi-fi sleep policy is set to 'never'. Wifi is off most of the time. Never used google latitude. Can any one tell me please the solution. :( If it cant be cured should I leave my phone on charge whole night?I have samsung galaxy s. my battery drains out in morning completely even I had slept for just 4 hours.?
just look for applications that might have been open.

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