Saturday, March 10, 2007

Laptop battery goes bananas

My Dell laptop battery is going bananas. I'm not sure what's really happened, but in the past three or four weeks, the battery life has gone from nearly two hours to only 45 minutes, right after being fully charged.

The laptop is about 18 months old. Since about five months ago, I started using a docking station at work. It pretty much charges my laptop every time I station it there - there's no option to unplug the power while using the dock. Before that, I always tried to "empty" the battery before I put the plug in.

The previous laptop, a Vaio, was even worse. Within two years the battery had pretty much gone; couldn't use it without plugging in the power. In this case, I also always tried to empty the battery before charging it.

Somehow I think using up the battery before charging it will keep the battery lifetime long. Like what people say about cell phone's battery. But does it?

Here' what Battery University says about lithium-based batteries. I'm too ignorant to check what kind of batteries there are for laptops and cell phones, but I assume most, if not all, of them are lithium-based.

Battery University? Yes. "Battery University is an on-line resource that provides practical battery knowledge for engineers, educators, students and battery users alike. The papers address battery chemistries, best battery choices and ways to make your battery last longer."

The battery prefers a partial rather than a full discharge. Ah, totally the opposite of what I thought. It further says "A lithium-ion battery provides 300-500 discharge/charge cycles. The battery prefers a partial rather than a full discharge. Frequent full discharges should be avoided when possible. Instead, charge the battery more often or use a larger battery. There is no concern of memory when applying unscheduled charges".

A lithium-ion battery in use typically lasts between 2-3 years. So we should expect to replace either the device or the battery (which is also expensive) after a couple of years.

The speed by which lithium-ion ages is governed by temperature and state-of-charge, as shown in the table below. (got to click to see, it's too small!)

The voltage level to which the battery is charged is also important, but it seems to be out of users' control.

The university further provides simple guidelines to prolong the life of lithium-based batteries:
  • Avoid frequent full discharges because this puts additional strain on the battery. Several partial discharges with frequent recharges are better for lithium-ion than one deep one. Recharging a partially charged lithium-ion does not cause harm because there is no memory. (In this respect, lithium-ion differs from nickel-based batteries.) Short battery life in a laptop is mainly cause by heat rather than charge / discharge patterns.
  • Batteries with fuel gauge (laptops) should be calibrated by applying a deliberate full discharge once every 30 charges. Running the pack down in the equipment does this. If ignored, the fuel gauge will become increasingly less accurate and in some cases cut off the device prematurely.
  • Keep the lithium-ion battery cool. Avoid a hot car. For prolonged storage, keep the battery at a 40% charge level.
  • Consider removing the battery from a laptop when running on fixed power. (Some laptop manufacturers are concerned about dust and moisture accumulating inside the battery casing.)
  • Avoid purchasing spare lithium-ion batteries for later use. Observe manufacturing dates. Do not buy old stock, even if sold at clearance prices.
  • If you have a spare lithium-ion battery, use one to the fullest and keep the other cool by placing it in the refrigerator. Do not freeze the battery. For best results, store the battery at 40% state-of-charge.
Source: Battery University