MBP Battery Draining Overnight

When running OSX and then shutting the lid of the MBP, this will put the unit to sleep correct?

When I shut the lid, the apple logo went off and the light indicator on the front pulsated. The battery was at 100%. On the following day, whenever I opened the MBP and logged in, the charge was at 82%. I thought it was meant to be "sleeping/hibernating".

Hardware fault? Battery? MBP?
Failed attempt to sleep? This doesn't seem to be the case as it was perfectly quiet, no fans and an absence of hard drive spinning.

Sleep mode does not translate into zero battery usage. It simply means that it is merely maintaining enough energy to keep the memory alive (among other things) so that when its ready to "wake up", you can pick up where you left off instead of starting with a fresh reboot. Just because the hard drive/processor fans aren't going doesn't mean there's other things still being fed some juice

kevin hit the nail right on the head. Sleeping is like a very low power state. Think about it, the light in the front is still glowing and all of the information is still stored in RAM (which requires voltage to keep working, take that away and it clears out). Those things need some sort of energy to keep running, and that's exactly why your battery is slightly drained when you open it in the morning.

You want zero battery drain overnight? Then turn it off.

Drain

I echo the sentiments of Kevin and Kash and would like to add that you can leave your computer in sleep mode for 5-7 days depending on the model, RAM installed, etc..

Thus it would make sense that you lose 18% in a day (that would last about almost 6 days in sleep mode). For full battery information on the specs and health look into CoconutBattery or iStat. I use both.

Final thought, if you are going to bed and put your computer into sleep, why not leave it plugged in over night while in sleep? No battery drain, plus quick boot from sleep mode. Just a thought.

I am aware that power is still being consumed though I have this mentality that 18% is a lot. Thank you for confirming though. Much appreciated