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Ask Max: Why is my battery life dying?

Asked on 09/10/2007:

I got a refurbished Aluminum PowerBook in June from PowerMax, but in the last couple of days the battery life has dramatically reduced to lasting only 15 minutes or so. What is happening?


When a laptops battery stops charging there can a few things at the root of the problem. Interestingly, the most common culprit is an under-powered power adapter. Apple has a habit of using cosmetically similar power adapters with different wattage ratings. Most iBooks will only need a 45 Watt power adapter, but many PowerBooks need a 65 Watt power adapter. Both the 45 and 65 watt Apple adapters are identical, and to further complicate the matter, a 45 watt adapter will look like it's functioning perfectly on a PowerBook. The problem is that despite appearances, a 45 watt adapter only runs the computer and barely charges the battery. This causes a short battery runtime like you are experiencing. The only way to see what adapter you have is to look on the edge of the adapter. It will have a 45W or 65W marking. You would think with the confusion from the old adapters, that Apple's new MagSafe adapters would all be the same wattage. Sadly Apple does the same thing with MacBook/Macbook Pro adapters as they did with iBook/PowerBook adapters. The MacBooks use 60 Watt adapters and the MacBook Pros use 85W adapters.

Even though most power adapters are linked to the right computer from the factory, sometimes refurbished or pre-owned computers end up with mixed-up adapters during the re-box process. If you find that you have the wrong adapter, it is just a matter of contacting your salesperson for exchange information.

The other possibility is that the battery has aged to a point of losing life. Rechargeable batteries can only be recharged a set amount of times before they start lose life. After that point, the battery will have an increasingly shorter run time on a full charge. Batteries are tested before resale, but in some rare instances they are closer to end of life then indicated in the testing process. This would again be covered for a period of time and you can contact your sales person for your options.

The last possible cause is faulty power management. This is the least likely possibility and there are two parts to it. There is a PMU reset that will clear bad settings. Here is are some links to reset instructions for a variety of Macs:

If that fails then it could be power management hardware, and that needs to be worked on by an authorized service center.

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