Newbie Mac tip: After over two years of use mostly as a desktop system, plugged in to house current, my Powerbook now only gets about an hour and ten minutes of use on a single battery charge before popping up the 5-minute warning. Our newer iBook gets a whopping 4 to 5 hours on a single charge, and I can't help but be a little jealous. Apple claims that iBooks get better battery life than Aluminum Powerbooks, which I believe. They also claim a Powerbook should get 4 hours on a single charge, which seems unrealistic, though the supernatural behavior of the iBook is something to aspire to. I should be getting a couple of hours on a charge, at least. I believe it's time to replace the battery.
Quite a bit of battery advice is based on rumor and mysticism, but the general consensus seems to be that rechargable batteries last the longest when each charge is mostly depleted before the battery is charged again. I typically use my Powerbook plugged in most of the time, which, I now know, is very likely to wear out the battery faster. Sometimes rechargable batteries can be "re-conditioned", with a complete discharge (push past the 5-minute warning until the Powerbook falls asleep and won't wake up again) followed by a full charge. Sure enough, doing so added about 20 minutes to my battery meter's "time" display.
To discharge a Powerbook/iBook battery in the computer, make sure it is not connected to power, then disable the energy saving features. If the battery meter is in your menu bar, click on it, then select "Better Performance". Otherwise, open System Preferences from the Apple menu, select Energy Saver, and choose "Better Performance" from the Optimization drop-down. This will prevent your laptop from conserving energy by shutting off the display while you're not at the keyboard. Leave your computer on until it falls asleep, and cannot be woken with a keypress. You can confirm the battery is depleted by pressing the button on the battery beneath the computer. Connect the power and leave the computer asleep until it's fully charged. (Don't forget to change back your Energy Saver settings, so when you're using it on battery power it will use the "Better Battery Life" setting.)
I noticed during the discharge that I did indeed get the 5-minute warning as soon as the battery meter ran down, but the computer stayed on for a good 30 minutes past the warning before it konked out. Without a reliable warning, I can't really use that extra time, but it indicates that either it's intentionally cautious about when it gives the warning, or my battery has gotten worse at reporting the actual charge remaining.
The best advice seems to be to take the battery out if I'm going to leave the Powerbook plugged in for extended periods of time. The Powerbook will run fine without a battery if plugged in, and the battery will last longer. Along these lines, it appears it is best to keep a partial charge in an unused battery: not a low charge, and not a full charge.
A typical (Aluminum) Powerbook battery has a capacity rating of 4800 milliamp-hours (mAH). That is, if the computer draws an average of 1200 milliamps of current as it runs, it ought to be able to do so for 4 hours. Mac OS X can report what it believes the capacity of the battery is using the
ioreg command. The following command runs
ioreg, and pulls out just the battery information from the million other things it reports:
ioreg -l | grep IOBattery
On our iBook, the "Capacity" it reports is about 4650, supposedly the number of milliamp-hours the battery can support. When I first started looking into the problem with my Powerbook's battery,
ioreg reported a "Capacity" of 1950. After I did a single re-conditioning pass, it read 2450. This shows the operating system is keeping track of this value to ensure the battery meter stays accurate. This also shows that re-conditioning actually did something. But it's still not close to 4800, and I'm not sure it ever will be again with this battery.
I'm curoius to know what
ioreg says for other Powerbook users with batteries new and old. This review of a third-party (non-Apple) Powerbook battery mentions
ioreg reports 4685 mAH for the battery on a full charge, and also says they never see more than two and a half hours in typical use. Googling for IOBatteryInfo shows other anecdotal reports along the same lines, with nicer numbers for new batteries than for old.
Powerbooks support battery swapping: put it to sleep, take the depleted battery out, put a charged battery in, wake it up and keep working. If I ever expect to be away from an outlet for more than 2:30, and I really need my Powerbook for longer, I could get a standalone battery charger, charge my old battery and well as my new one, then carry them both. I've only had one situation where this would have been handy, and that was because I forgot to bring my power brick to the library one day. But it's nice to know it's an option. MacSales.com sells Apple batteries, third-party batteries, and standalone chargers.
An extra hour might be worth the cost of a new battery in my case ($100-$150). Still, the power management on the newer iBook seems impressive, and I would hope the latest "hi-res" Powerbooks and the forthcoming MacBook Pros can live up to the challenge.
Troubleshooting the PowerBook Battery has some good info.