(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
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:
Serial Number: Sony-ASMB012-3735-19c
Device name: ASMB012
Pack Lot Code: 0003
PCB Lot Code: 0000
Firmware Version: 102a
Hardware Revision: 0500
Cell Revision: 0303
Charge remaining (mAh): 1889
Fully charged: No
Full charge capacity (mAh): 1925
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
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:
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
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
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
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
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)
||Charge remaining (mAh)
||Full charge capacity (mAh):
|7:06 24% RED
|7:09 20% RED
(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)
||Charge remaining (mAh)
||Full charge capacity (mAh):
|7:10 19% RED
|7:45 am 99%
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 )
- 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.
- 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.
- 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.
- 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.
- Turn off the computer or allow it to sleep for five hours
- 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
Full charge capacity (mAh): 5589
Cycle count: 4
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
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
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 24 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.
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© 2011-06-18 Anthony Lawrence