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Give your battery a thorough checkup
Authored by: Anonymous on Mar 13, '03 10:52:42PM
Interesting comment, and it sure speaks better of my own iBook capacity ... it makes me wonder if the Knowledge Base article is wrong.

XBattery reports my capacity as 3.544 Ah and my voltage as 16.058v. Multiply the two together and I get 56.9096 watt-hours, which is actually a little above what the Apple Store describes as the capacity of the battery: "A 56-watt-hour rechargeable lithium ion battery that provides up to 6 hours of operation depending on battery saving features used and system configuration. This battery is compatible only with iBook 14.1" TFT displays."

Here are the numbers I grabbed from the battery descriptions at the Apple store:

iBook (12.1") - 42 watt-hours
iBook (14.1") - 56 watt-hours

PowerBook (12.1" TFT) - 47 watt-hours
PowerBook (15.2" TFT) - 61 watt-hours
PowerBook (17" TFT) - 55 watt-hours

Let's play this multiplication game with some of the numbers above from the original hint:

voltage=11928 flags=4/0x004 amperage=1023 capacity=4192 current=3692 [88.1%]

50.0022 watt-hours on a 12.1" iBook. (Possibly erroneous, considering a 12.1" iBook battery supposedly has a 42 watt-hour capacity.)

voltage=16670 flags=5/0x005 amperage=1200 capacity=4017 current=3928 [97.8%]

66.9634 watt-hours on a "newer machine" -- it's close to the stats of a 15.2" Powerbook.

voltage=16564 flags=5/0x005 amperage=1200 capacity=2942 current=2931 [99.6%]

48.7313 watt-hours on a TiBook; this could be a 12.1" TiBook.

voltage=10943 flags=4/0x004 amperage=983 capacity=1814 current=1570 [86.5%]

19.8506 watt-hours on a 500 mHz iBook. Whether it's compared to the 42 watt-hour or 55 watt-hour figure, this is a depleted battery.

voltage=12236 flags=5/0x005 amperage=1200 capacity=219 current=214 [97.7%]

2.6797 watt-hours on a "very sick" battery. Yup, it's sick. :)

Now, let's look at the ones in the comments:

leffo: voltage=12620 flags=5/0x005 amperage=1200 capacity=4148 current=4139 [99.8%]

52.3478 watt-hours on leffo's iBook.

wilkens: voltage=12400 flags=5/0x005 amperage=1200 capacity=4149 current=4091 [98.6%]

51.4476 watt-hours on wilkens' iBook.

wOOge: voltage=11901 flags=7/0x007 amperage=1200 capacity=2493 current=1545 [62.0%]

29.6692 watt-hours on wOOge's iBook.

lockley: voltage=12313 flags=4/0x004 amperage=1200 capacity=1431 current=1426 [99.7%]

17.6199 watt-hours on lockley's laptop.

Enkerli: voltage=12254 flags=4/0x004 amperage=1200 capacity=2882 current=2882 [100.0%]

35.316 watt-hours on Enerkli's iBook.

tamenti: voltage=11384 flags=4/0x004 amperage=1110 capacity=2054 current=1690 [82.3%]

23.3827 watt-hours on tamenti's iBook.

Joegrind: voltage=15817 flags=4/0x004 amperage=1019 capacity=6236 current=5593 [89.7%]

98.6348 watt-hours on JoeGrind's Powerbook. (Yeesh! That's off!)

xchanyazy: voltage=12442 flags=5/0x005 amperage=1200 capacity=3098 current=3089 [99.7%]

38.5453 watt-hours.

mattmoss: voltage=12389 flags=5/0x005 amperage=1200 capacity=1752 current=1746 [99.7%]

21.7055 watt-hours.

dcheng: voltage=12540 flags=5/0x005 amperage=1200 capacity=3645 current=3645 [100.0%]

45.7083 watt-hours.


[ Reply to This | # ]
Make sure you're looking at average voltage
Authored by: magitekkn on Mar 14, '03 02:31:39AM

The important thing to remember while performing this math is that your voltage drops off almost linearly (it appeared to begin to drop more rapidly towards the end for me) therefore you should take the mean value of the voltage across the entire discharge cycle to get the proper value.

Looking back over my numbers, my high voltage at 100% charge is 16.7v, whereas my minimum was 13.9v. If my battery was able to hold 16.7v for the entire discharge cycle (I've never seen a battery capable of this personally) and held a 3.5Ah capacity, the power capacity would be 58.45Wh (note this is a 55Wh battery). However, if the battery held at 13.9 for the entire discharge cycle, there would only be 48Wh.

Now if we take the average of 13.9 and 16.7 we get 15.3v. 15.3v by 3.5Ah = 53.55, still close to Apple's rating for a new battery.



[ Reply to This | # ]