Hi, I am having a problem with my black macbooks battery. It seems that when the battery gets below 20% or so and I shut down the computer and I do not plug in the power adapter, the next time I try to start it up it will be dead even if it had about and hour of battery life left when it was shut down. I have to plug in the adapter in order to turn it back on. This doesn't seem to happen when the battery is charged above 50% before shut down. I don't know why but the battery is losing power even when it is shut down.