you prob have calibrated the battery properlly
the reason its constantly changing the time left is because of what your doing on the mac.
for example. if you turn on the mac, with no bluetooth or airport turned on, with no programs running, just having the computer on idle with brightness turned down lowest setting, volume off, backlit keyboads off. it will say it has 5 hours left. that means, it can keep being idle for 5 hours before it runs out of power in the battery
however if you had bluetooth,airport on, and had numerous programs running, and had ipods, external hard drives, etc plugged in, with brightness up full, backlights on, volume up then obviously its consuming more power from your battery therefore lowering the time left you have before all power runs out, using these settings, applications, and external hardware etc 🙂
so just try minimize the number of things your doing, if you can't then buy an extra battery to give you more time if your travelling, or if you have access to power then just keep it plugged in 🙂
the time remaining constantly changes depending on what you're doing on your macbook
hope that answers your question 🙂
