Estive lá, fiz isso. Meu 2007 MBP está em sua terceira bateria, que atualmente está no ponto "Service battery".
Se você não descarregar com muita frequência, certifique-se de calibrá-lo ocasionalmente, permitindo que ele percorra todo um ciclo de recarga de carga e descarga. Isso aumentará a estimativa do seu computador quanto à duração da bateria, o que geralmente tem sido uma coisa boa na minha experiência. Aqui estão as instruções da Apple :
Calibrating your battery ensures you get the longest possible running time from it. Calibrate your battery during the first week you own it, and then recalibrate it every two months. If you use your computer infrequently, it’s best to recalibrate it at least once a month.
Whenever you purchase new batteries, calibrate them as well. To calibrate a portable computer battery:
Plug in the MagSafe Power Adapter and fully charge the battery.
When the battery is fully charged, the light on the MagSafe Power Adapter connector changes to green and the Battery icon in the menu bar indicates that the battery is charged.
Allow the battery to rest in the fully charged state for two hours or longer.
You can use your computer during this time as long as the power adapter is plugged in.
With the computer still on, disconnect the power adapter and continue to use your computer.
When you see the low battery warning, save your work and close all applications. Keep your computer turned on until it goes to sleep.
After your computer goes to sleep, turn it off or allow it to sleep for five hours or longer.
Connect the power adapter and leave it connected until the battery is fully charged.
You can use your computer during this time.