New Battery for MacBook Pro

(Although this article shows information specific to Apple OS X and MacBook Pro equipment, much of the information here would apply to any laptop battery and also to many cell phones, MP3 players and so on.)

I bought this Macbook Pro three years ago this February. When I first got it, the battery life was decent, but not up to the advertised specs. At best I could only get two hours out of it. Because of that, I bought a spare a few months later - I figured that was a good thing to have anyway.

Some time after that Apple announced a battery recall for some units. Either neither of mine was among the problem units or I just can't remember swapping it out; I can't find any record of doing that. I think I might have gotten a new one but I'm not sure about that.. I am sure I didn't get two. Two hours isn't all that bad anyway and if I ever needed it, I had that spare, right?

Unfortunately, I wasn't aware that you have to USE Lithium-ion batteries - you can't just leave them in storage forever. Shortly after buying that spare, I forgot about it entirely - well, until I noticed that I could barely get a half hour of use from my battery.

One clue that I might have had a swap is shown in "About This Mac->More Info-> Power". It's not a bad idea to take a peek at this now and then:

 Battery Information:
 
   Model Information:
   Serial Number:	Sony-ASMB012-3735-19c
   Manufacturer:	Sony
   Device name:	ASMB012
   Pack Lot Code:	0003
   PCB Lot Code:	0000
   Firmware Version:	102a
   Hardware Revision:	0500
   Cell Revision:	0303
   Charge Information:
   Charge remaining (mAh):	1889
   Fully charged:	No
   Charging:	Yes
   Full charge capacity (mAh):	1925
   Health Information:
   Cycle count:	28
   Condition:	Check battery
   Battery Installed:	Yes
   Amperage (mA):	207
   Voltage (mV):	12603
 

That cycle count seems suspicious for a three year old unit. Apple's batteries page explains:

A charge cycle means using all of the battery's power, but that doesn't necessarily mean a single charge. For instance, you could listen to your iPod for a few hours one day, using half its power, and then recharge it fully. If you did the same thing the next day, it would count as one charge cycle, not two, so you may take several days to complete a cycle.

No matter what, you'd think I would have used up more than 28 cycles in three years. Apple says the batteries should be good for 300 cycles, so I had plenty of breathing room.

You WANT to cycle your battery now and then. Apple again says:

http://www.apple.com/batteries/notebooks.html

For proper maintenance of a lithium-based battery, it's important to keep the electrons in it moving occasionally. Apple does not recommend leaving your portable plugged in all the time. An ideal use would be a commuter who uses her MacBook Pro on the train, then plugs it in at the office to charge. This keeps the battery juices flowing. If on the other hand, you use a desktop computer at work, and save a notebook for infrequent travel, Apple recommends charging and discharging its battery at least once per month.

But not too often: Battery University warns:

Do not discharge lithium-ion too deeply. Instead, charge it frequently. Lithium-ion does not have memory problems like nickel-cadmium batteries. No deep discharges are needed for conditioning.

Well, whether I got lax on that or had a replacement at some point; overall I had three years of use before it got to this stage. I really couldn't complain, but obviously it was time for a change. I then remembered the spare, dug it out, and found it totally dead. With Lithium-ion, that's it: a dead battery really is dead.

Charging lithium-ion batteries at Battery University says:

Extreme low voltage must also be prevented. The safety circuit is designed to cut off the current path if the battery is inadvertently discharged below 2.50V/cell. At this voltage, most circuits render the battery unserviceable and a recharge on a regular charger is not possible.

There are several safeguards to prevent excessive discharge. The equipment protects the battery by cutting off when the cell reaches 2.7 to 3.0V/cell. Battery manufacturers ship the batteries with a 40% charge to allow some self-discharge during storage. Advanced batteries contain a wake-up feature in which the protection circuit only starts to draw current after the battery has been activated with a brief charge. This allows prolonged storage.

In spite of these preventive measures, over-discharge does occur. Advanced battery analyzers (Cadex C7000 series) feature a 'boost' function that provides a gentle charge current to activate the safety circuit and re-energize the cells if discharged too deeply. A full charge and analysis follows.

If the cells have dwelled at 1.5V/cell and lower for a few days, however, a recharge should be avoided. Copper shunts may have formed inside the cells, leading a partial or total electrical short. The cell becomes unstable. Charging such a battery would cause excessive heat and safety could not be assured.

So that's the end of that. It's heading for a recycling center and I had to buy a new one.

I ordered that directly from Apple. Yes, yes, I could have saved a few dollars buying somewhere else but these large battery packs can be dangerous and I just feel batter knowing that there's no chance I was getting a counterfeit.

Fedex delivered a stone cold package Thursday afternoon. I made sure that the new battery had warmed up before putting it into the MacBook. As explained at Lithium-ion safety concerns, charging a cold battery is bad:

Another safety issue is cold temperature charging. Consumer grade lithium-ion batteries cannot be charged below 0C (32F). Although the packs appear to be charging normally, plating of metallic lithium occurs on the anode while on a sub-freezing charge. The plating is permanent and cannot be removed. If done repeatedly, such damage can compromise the safety of the pack. The battery will become more vulnerable to failure if subjected to impact, crush or high rate charging.

So I had to wait a few hours before I put it in and let it charge up. I then let it run on battery and watched the System Profiler as it discharged. I unplugged it at 6:00 PM and it was at 70% 24 minutes later:

Discharging (running on battery)

(Negative amperage indicates battery is supplying power)

Note that I just did typical work throughout all these tests - writing text articles, searching Google, reading RSS feeds. I plugged it back in at 20% after it had run just a little over one hour - it could have run another ten minutes or so before giving the "Reserve" warning. I then watched it recharge.

Charging (power adaptor plugged in)

As expected, the system switches to a lower charge at 95% and it takes longer to get to the fully charged point.

Apple says you need these discharges to calibrate the battery. The recommended procedure for the MacBook Pro model involves leaving the system off for five hours:

(Calibrating your computer's battery for best performance )

1. Plug in the power adapter and fully charge your PowerBook's battery until the light ring or LED on the power adapter plug changes to green and the onscreen meter in the menu bar indicates that the battery is fully charged.
2. Allow the battery to rest in the fully charged state for at least two hours. You may use your computer during this time as long as the adapter is plugged in.
3. Disconnect the power adapter with the computer still on and start running the computer off battery power. You may use your computer during this time. When your battery gets low, you will see the low battery warning dialog on the screen.
4. Continue to keep your computer on until it goes to sleep. Save all your work and close all applications when the battery gets very low, before the computer goes to sleep.
5. Turn off the computer or allow it to sleep for five hours or more.
6. Connect the power adapter and leave it connected until the battery is fully charged again.

After cycle 4, I decided to do that. In preparation, I set my system back to its default "hibernate to disk" mode:

 sudo pmset -a hibernatemode 3
 

I normally have that set to 0 (hibernate to ram) to make the "wake up" time quicker. That's safe to do when the system is plugged in, but if I'm going to let it fully drain as this requires, I want it on disk - just in case. The Mac fsck has never failed me before when I have accidentally let this die, but why look for trouble?

So, at 3:20 PM I unplugged with a charge of 57% and this Charge Information:

   Charge remaining (mAh):	3227
   Fully charged:	No
   Charging:	Yes
   Full charge capacity (mAh):	5589
   Health Information:
   Cycle count:	4
   Condition:	Good
   Battery Installed:	Yes
   Amperage (mA):	3111
   Voltage (mV):	12132
 

I worked until it was forced to sleep. That was just about 5:00 PM. I managed to get a look at the System Profiler after the battery indicator said 0% - supposedly there were 21 mAh remaining.

At some point the system has to give up and shut down. I don't know when the pulsing sleep LED finally went off; it wasn't off at 10:00 PM when I last looked. It was off in the morning, so I plugged back in and let it charge.

Notice that the usable battery time increases with each cycle. Is it that the battery is learning how much reserve it really has or is it simply getting a better charge? Either way, my usable time is getting closer to that three hour spec.

After this last cycle, I did a 24 minute unplug from 100%. Again, I did normal work during the period. After 20 minutes, the indicator only dropped 14% and the remaining charge dropped 945 mAh. Contrast that with dropping 30% and 1681 mAh after 24 minutes when I first put this in. This should be very close to 3 hours now.

I'll update this post from time to time as the battery ages so we can see how things change.