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laptop batteries

By jbraylor ·
I found some good advice here on trying to revive a "dead" laptop battery. I unfortunately left my battery alone for about 1 year. No charge can hold at this time in the battery. I saw in the last discussion that by passing a 100 ohm resistor over the battery and using a bench charge to force current into the battery, I can probably make it come back. It's still a new battery. How can I hook up a resistor to the battery? Do I take it to a specialized shop? Please advise. Thks.

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Battery Advice....from an expert

by GuruOfDos In reply to laptop batteries

Battery technology is a black art, but as I have been involved in portable power in all it's forms for many years, let me give you some pointers!

There are 3 types of cells in notebook batteries.

1. Nickel-Cadmium (NiCd)

The oldest kind, and rarely found on any notebook since about 1995. This type you can refresh by the bench charger and 100R resistor trick, but a NiCd battery left discharged for any extended period of time will suffer drastically and not hold a charge easily. You then have to bench charge, and then fully discharge several times to get the capacity up again, but after 200 cycles or more, don't expect better than 50% capacity. After 300 cycles, NiCd's have had it.

2. Nickel-Metal Hydride.

More common in notebooks, and do not suffer from memory effect. They have a greater charge density and a cell with identical dimensions to a NiCd battery can often pack double the Ah (Ampere-hours) rating. They have to be charged at a constant voltage and a constant current, are good for perhaps 400 cycles but suffer from one major drawback. Ni-MH cells have a habit of 'failing' because of crystalisation of the electrolyte in the cells. They end up having a high resistance and therefore cannot take a charge or don't produce the running time you would expect. The remedy, believe it or not, is to remove the battery pack from the notebook and give it a good smack against a hard surface such as a wall or floor. This breaks up the crystal structures that form in the electrolyte and allow the battery to regain most of it's original capacity. A typical lifespan of an Ni-MH battery pack is some 400-500 cycles, but this is seriously reduced if the pack is not completely recharged.

3. Lithium-Ion

Used in most modern notebooks (and mobile phones). DO NOT ATTEMPT to charge these using ANYTHING other than the supplied charger (or notebook power supply). Two reasons. These batteries have an energy density some ten to fifteen times greater than Ni-Cd's, and unless charged to extremely precise specifications, can fail with remarkably dramatic results. Li-Ion batter packs, if you open them up, have a very complex circuit built into them which not only monitors cell temperature during charging, but regulates the charging in precise voltage and current stages, but also shuts down and disconnects the battery pack in event of over discharge. Iff the terminal voltage of each cell (3.2 volts as oposed to 1.2 for Ni-Cd or 1.25 for Ni-MH) drops below about 2.5v under discharge conditions, the cell is unable to be recharged. The monitoring circuit protects against undervoltage and excess current as well as overcharge and short circuit, and the circuits inside each pack are specific to the notebook and charger circuit.

The long and short of it is this....if your Li-Ion battery no longer works, forget CANNOT be recovered. If you don't believe me, I'll email you the photographs of a colleague who DID try a bench charger on one of these packs. He will have the scars for kidding! An incorrectly charged Li-Ion cell is like a stick of dynamite.

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