PowerBook G4 Battery Buying Guide

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This guide will explain the basics of Lithium Ion battery technology and the criteria that should be considered when purchasing a used battery for Titanium PowerBook G4 computers. The basic information is also useful for any system that uses Lithium Ion (Li-Ion) batteries. Buying a used PowerBook battery can be a great bargain or a terrific waste of money. Take a few moments to educate yourself on Lithium Ion batteries and the information that should be in a battery listing before purchasing a used PowerBook battery.

Lithium Ion batteries have been standard in all PowerBooks beginning with the Titanium G4 models and continuing with the current family of MacBook Pros. Titanium PowerBook batteries all have the same form factor and can be used interchangeably. Apple PowerBook batteries have model numbers such as: M6091, M8511, M8244, A1012, etc. The difference between the various model numbers is the absolute capacity of each model; the M6091 battery has a capacity of 3600 mAH whereas the M8511 has a maximum capacity of 4000 mAH. There are also third party vendors, such as Newer Tech and BTI, that manufacture PowerBook batteries that have even greater capacities.

Li-Ion batteries combine the best qualities of alkaline batteries with the best qualities of rechargeable batteries. Li-ion batteries provide constant voltage during discharge and do not suffer from the memory effect that plague Ni-Cd batteries. Li-ion batteries also provide the highest available energy density of any available battery technology (i.e. provides more power per ounce as compared to NiMH or NiCad) Li-Ion batteries also have a low self-discharge rate (about 5% per month) compared to Nickel Metal Hydride (about 30% per month) or Ni-Cd (about 20% per month). A little known characteristic of Li-Ion battery technology is that Li-Ion batteries lose approximately 15% usable capacity each year (depends upon storage temperature). Because of their characteristics, PowerBook batteries can operate for between 300-500 cycles and last for about 5 years from the manufacture date.

OS X can accurately determine the charge state, capacity, number of cycles on the battery, discharge voltage and amperage based upon the information provided by the battery electronics. Mac OS X utilizes this information to provide your PowerBook with the estimated operating time and estimated capacity. Using Apple's System Profiler utility, any PowerBook user can readily determine the full charge capacity, remaining capacity, voltage and cycle count (requires at least 10.4.3).

Another feature of PowerBook batteries is the built in fuel gauge. Just push the silver button and you can readily determine the charge state of the battery. The fuel gauge DOES NOT provide any information regarding the health (or capacity) of the battery. It only indicates the battery's charge state. If the battery only holds a 360 mAH charge, all 4 lights will illuminate, but the battery only has 10% of it's original capacity. Another quick factoid is that only genuine Apple batteries keep the LEDs illuminated for several seconds after the button has been released. As far as I know, the LEDs extinguish as soon as the test button is released with all third party batteries.

An average PowerBook battery operating time is a tricky number to accurately quantify. Battery operating time is dependent upon power settings selected by each individual user and the processor speed of the PowerBook. A battery that operates for 2 hours on a PowerBook with maximum energy saving options selected (e.g. dim screen, reduced processor speed, disk spin down, etc.) may only operate for 1 hour on the same PowerBook with no energy saving features selected.

A simple test that I use for determining PowerBook battery capacity is to play a DVD. This is the most energy intensive test that you can perform on your PowerBook. I usually set up this test with all energy saving features disabled (disk spin down = off, full bright display, processor performance = highest, no sleep, etc.) This provides the worst case scenario. Normal operating conditions will usually be better than my test conditions. I would rather have a customer get a battery that was tested to operate for 90 minutes and actually operates for 2 hours (under normal conditions), than for the customer to get a battery that only operates for 1 hour.

Here's What You Should Consider Before Purchasing a Used PowerBook Battery:
  • Titanium PowerBook G4 batteries are interchangeable between any of the different processor speeds. An A1012 battery will work in a 500 MHz PB as well as a 1 GHz PB. The main difference between the model numbers is the battery's capacity.
  • Li-Ion batteries have a 300 to 500 cycle lifetime. Mac OS X Tiger (10.4.3 and on) allows you to monitor the number of cycles on a battery using the System Profiler. Try to avoid a used battery that has a very high number of cycles on it.
  • A new PowerBook battery should be able to play a DVD for about 2 and a half hours. A good used battery should be able to play a DVD for at least an hour and a half. A used battery that plays a DVD for about an hour and a half will probably operate for over 2 hours under "normal" operating conditions (this is just an educated guess based upon my experience).
  • Li-Ion batteries tend to lose about 15% capacity each year, depending upon storage conditions. Try to avoid purchasing a battery that is more than 5 years old.
  • Be cautious if you're considering a battery where the listing doesn't provide any test data. It's a simple matter to test the battery and provide operating conditions and run time in the listing.
  • Be cautious when a battery listing makes claims like "holds full charge" or "all 4 lights illuminate" . As I stated above, this means virtually nothing regarding the health of the battery.

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