Li-Ion battery life

2007/12/12 by Lassi A. Liikkanen

Recharge science: Taking care of Li-Ion batteries

This articles provides advice on how to prolong your portable device's (laptops, Ipod MP3 players, cameras, etc.) battery life. It is important to realize that Lithium Ion (Li-Ion) batteries are unlike older techniques and require different kind of care.

A short history of rechargeable batteries

Everyone knows what a battery is. At least, on the surface. However, the batteries we use in laptops, cameras, or such, most often contain several batteries, called cells. The cell is the heart of battery and the number cells connected in parallels and serials determines the voltage and capacity of the battery. The Li-Ion battery is a relatively new invention in the category of rechargable battery cells. Currently used and popular cell types are listed below, in order of appearence (year indicates production, not invention). The order of appearence is directly linked to increasing order of energy density:

  • 19??: Lead and sulfuric acid
  • 1946: Nickel cadmium (NiCd)
  • 1990: Nickel metal hydride (NiMH)
  • 1991: Lithium ion (Li-ion)
  • 1996: Lithium ion polymer (Li-ion polymer)

Acid (nowadays gel) is still used in vehicles, but as of 2007, new electric appliences mostly rely on some lithium-type battery. To apply the tips below, make sure your battery is Li-Ion, because especially nickel-based batteries should be treated very differently (deep-cycles, freeze, etc.). According to BatteryUniversity article, all the same rules apply for lithium polymers as well.

Li-Ion facts

Li-Ion batteries were a big advance in battery technology. Their chemical properties provide high enerdy density allowing small and powerful packs, but on the down side is that if they are treated poorly, they can die quickly or on the other end, even explode! Explosions have happened and actually, you cannot take a huge (ove 96Wh, see BU page) Li-Ion battery on board an airplane because it is a potential explosive! Li-Ion battery should live for over 300 charge cycles (2-3 years) but after that it will die of old age, no matter what you do. Few facts in contrast to what you may have learned from the nickel era:

  • Li-Ion batteries do not need a priming charge when first taken in use (unlike Nickel)
  • Li-Ion batteries don't really support quick charge. The cells of a battery always aim for the same voltage (4.2V), so charging any Li-Ion properly from 20% to 100% takes always appr. the same time!
  • Li-Ion batteries do not benefit from completely discharging. If the cell goes very low voltage (below 2.5V) it will go beyond normal means of recharging and dies. However, full discharge/charge can be used to estimate the real capacity of a battery (although not refresh it)
  • Li-Ion batteries do not have a 'memory' like nickel bro's

Taking care

In use

  • Don't heat it. It may not explode, but internally it may more quickly corrode. In a laptop constantly running in the mains, take it off (especially if you've got UPS).
  • Charge it often according to the following guidelines
  • Don't charge it too often. If are usually connected to the mains, you should lower the threshold of recharge, that is, as the charge slowly dissipates during the time when the device is not in use, it will have an internal threshold, say 98 %, when the charger begins to recharge it. By lowering this threshold to 94 % will reduce the number of (unnecessary) recharge cycles while attached to a power cord.
  • Don't constantly discharge completely. This will surely reduce the life-cycle.
  • Let it discharge sometimes. BatteryUniversity recommends running battery to the point of very low indication every 1 / 30 cycles will reset the gauge so your device will know the capacity more accurately.
  • Together these point out that in normal office use, keeping a battery connected to the computer and running the computer primarily on AC will kill the battery, usually in one, one and a half years.

In storage

  • Don't buy, unless you need it. Batteries age even when not in use, inspect the manufactoring date of the battery you are about to buy.
  • Don't freeze it. The battery electrolytes may actually freeze, if you've acquired a battery you don't intend to use, store it in a fridge more preferably.
  • Don't store it fully charged. In Li-Ion battery will age (lose capacity) more rapidly if fully charged, and for storage, 40% charge is suggested.

References

BatteryUniversity: Part One

Wikipedia on Rechargeable batteries

Wikipedia on Li-Ion

Related content:
Programming Harmony 1, 2012/11/26

How to recover from failure to boot newly assembled PC, 2009/03/29

Comparison for two RAID 0,1 Network attached storage devices, 2009/01/31

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Keywords: [electronics] , [computers] Document's status: Ok (Document dates explained)

This document created: 2007/12/02
Modified: 2007/12/12
Published: 2007/12/02


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