Saturday, April 11, 2009

Laptop Battery Care and Feeding

This article briefly discusses how to best take care of a Lithium-Ion laptop battery.

Lithium-Ion batteries are not the same as older NICAD (Nickle Cadmium) batteries and they should be treated differently for longest life.

Related Article:
Third-Party Replacement Battery for the Dell XPS M1530

In summary:
  • Lithium-Ion Batteries do not have "memory"
  • Avoid numerous deep discharges
  • Ideally, re-charge when at 30 to 40% capacity
  • Re-calibrating a battery / new batteries
  • Avoid heat (hot cars, etc)
  • Consider removing the battery when using AC power for long periods
  • The battery will age and wear out; a fact of life
Unlike NiCad batteries of yesteryear, Lithium batteries do not have "memory" (where the battery "forgets" how to hold a full-charge - NiCads had this problem). Deep discharges will not keep the battery healthy and deep discharges actually damage Li-Ion cells.

Although Lithium batteries do not have memory, they will age and loose capability and this is true of all rechargeable batteries. After 200 charge cycles, the battery will have a noticeable decrease in capacity. After (400-500) charge cycles, the battery will likely need replacing. For most users, this will happen after about 2 to 3 years, depending on your tolerance on recharging.

Abusing the battery (with numerous deep discharges or continuous heat) will hasten its demise, as will keeping the battery fully-charged in a heated environment, such as inside of a laptop. A partially-discharged battery inside of a warm laptop will age better than a fully charged battery under the same conditions.

If your laptop is normally plugged into AC power and seldom strays, consider removing the battery -- mainly to protect it from the heat. (However, if there is a power-outage, the battery will not protect your work). This does not mean you shouldn't use the battery; after all, it does have a purpose in life.

Real-World Laptop Battery Life

My Dell XPS M1530, when new, came with a standard 6-cell Lithium-Ion battery, would last about 2.0 to 2.5 hours; running under Vista's Moderate Power Settings. The larger 9-cell battery gives 3.5-4 hours.

Now that this laptop is 18 months old, the 6-cell battery capacity has fallen to .00005 hrs; a noticeable decline. In other words, batteries age, even when treated with some respect. See this article on buying a replacement battery.

Battery Meter Accuracy
ReCalibrating a Battery

Most Lithium-Ion batteries have an onboard LED meter showing the battery's capacity. This circuitry is also what Windows queries for the System-Tray report.  This circuit can get out of calibration and can report incorrect values.

Recalibrating does not improve the battery's capabilities; it only aligns the meter's reading with the battery's actual charge.  If the meter is out of calibration, Windows 7 will assume imminent failure and will hibernate a battery-powered laptop, even if the battery is "charged."  You will see this problem when you have what you know is a fully-charged battery, but Windows will suddenly report x% power remaining and will warn you to re-charge.

To re-calibrate:

1.  Allow the battery to fully discharge, letting the laptop shut-down.

New batteries sometimes will not charge properly, stopping at (15% or similar number), because they are in an "unformed" state.  Symptoms:  The battery may stop charging before fully-charged.  If this happens, power off the computer, remove the battery and re-insert.  The charge cycle should begin again. This may happen several times during your first charge.

2.  Remove the battery and re-install.

3.  Allow the battery to fully-charge; confirm the system tray shows "charging."
Once fully charged, confirm by checking the meter on the back of the battery (most batteries have this feature).

4.  Do this cycle twice for new batteries and about every 20 or 30 partial cycles (4 to 5 months) for older batteries. Yes, this violates the recommendation above against deep discharges.

If a battery shows fully charged after only a few minutes, when you know it is not, re-calibrate. If this is still a problem, the battery may need replacing.

Long Term Storage:

For long-term storage, discharge battery to 40 to 60% and store in a cool location, such as a refrigerator, not a freezer. Use a plastic bag to keep moisture at bay. A (room temperature) battery looses about 2% of its charge per week due to environmental and chemical changes.  Because of this, an idled battery can deep-discharge without your knowledge an Li-ions do not like this.

Periodically, every two or three months, a stored battery should be re-charged and partially discharged before being placed back into storage.  This is nuisance and may be a good reason not to have too many spare batteries.

Rapid Chargers
From personal experience, rapid (Fast) chargers kills Lithium-Ion batteries; much heat is generated. This would be true with those AA-battery chargers, as well as larger equipment, such as laptops and power-tools.

Other Sources and topics:
Third-Party Replacement Battery for the Dell XPS M1530
Battery University (very interesting)
Online Laptop Batteries
MIT Develops new Rapid Battery
HP Extends Laptop Battery Life 24 hrs.
Wikipedia: NiCad