The care and keeping of laptops and batteries

Question: from msk6261
Do you destroy the "memory life" of a rechargable battery when you leave it plugged in all the time? Is it best to let the battery drain and recharge on a regular basis? Is it OK to almost always have the notebook plugged in? What is the best practice for keeping the longevity of the battery time and overall battery life?

Answer:
It depends what you mean by "memory life". There are two types of memory associated with notebook batteries:

a) the type of memory that prevents a battery from physically taking charge

b) the "digital memory" deterioration that causes notebooks' charge level calibration to get progressively less and less accurate

Type a) affects only NiMh/NiCd battery types, whereas type b) affects pretty much all battery types where the laptop monitors charge levels - including those of Li-on batteries.

The resulting effect of digital memory loss is that your notebook's power meter misreads the charge level in the battery, reporting the wrong % charge remaining figure to you in your taskbar and, reporting the same to your power management program!
Over time this inaccuracy may get greater until eventually your battery is virtually useless.
Note that some notebook manufacturers provide better power mangement than others: Dell, IBM/Lenovo and Toshiba seemed to suffer a great deal from this problem. They seem to all have one thing in common: once the battery is charged they don't stop charging and switch to AC power. Instead, they continue to run off battery power while charging, resulting in continuous charge/discharge of the battery. This is exceptionally bad as far as power meter calibration goes! There are dozens of Thinkpads owned by my employer that have very little battery life as a result of this flip-flopping of charge/discharge. You can identify this problem if your power meter reports 100%, 99%, 100%, 99%, 98%, 99%, 100% etc. over a period of just a few minutes.
Some laptops will respond to the detection of a battery becoming fully charged by cutting off charging and running from AC while plugged in. This will help to extend the life of the battery (yes, Li-Ons too, they have a limited number of full discharges during their lifetime).

Even if your laptop manages charging better, you will still find your power meter goes out of calibration over time. Although it is not recommended to regularly fully discharge your battery, you should periodically fully discharge it and fully charge it (don't leave the battery for an extended period with no charge in it). This will allow proper calibration of the power management program and ensure that the power meter gives a more accurate reading. It is important to do this whenever you notice a deterioration in the normal operating time of your battery - if you leave it too late then you will never get close to the times you once did. Note: this has nothing to do with Ni-MH/Ni-Cd battery memory loss! Although it will work for them too, for a different reason.

For Mac users:
OS 9 and OS X comes with a digital memory reset function to get around the calibration problem (reset NVRAM or something like that). Unfortunately there doesn't seem to be such a utility available from other laptop manufacturers

You can read everything you need to know about (li-on) battery care at:
http://www.rm.com/_RMVirtual/Media/Downloads/Lithium_Ion_Batteries_Care.doc
http://www.batteryuniversity.com/parttwo-34.htm
also try:
http://monkeyfilter.com/link.php/7094
http://www.laptop-battery.org/batterytips.html

and http://www.macintouch.com/laptopbatt.html (for Mac users)

Hope this helps.