Battery leaks on macbook?

I use my macbook a lot lately without connecting it to a power outlet. I disconnect it from power supple in the morning and put it in my backpack, and after 3 hours I waked it up by opening the lid and I notice the battery is at 95%. The battery is pretty much out of power after about 4 hours of use with airport on for wireless connection, and at the lowest brightness. Is it possible there is a battery leak, or is this normal? The battery is at 99% health and 40 cycles. It was went down to 96% health before, and it came back to 99% after I calibrated the battery.

 

This is completely normal.
Sleep mode draws a small amount of power thus over time it will eventually drain out. If long battery life is critical, then shut down instead of putting it to sleep.
For a macbook 4h is about right. The newer mb pro's with the inbuilt battery will get about 6h or more.
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ps battery health will often fluctuate quite abit by its self. For eg, in the space of a week, my mb battery went from 92% back up to 99%, without me doing any calibration, just thru normal usage. If it dips below 85% for a prolonged period then its worth getting it looked at by apple or buying a replacement battery.

 

Refer to the Battery Guide for more information on these types of batteries.