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I have received some Li-ion batteries which were originally used in Asus A2 Laptop battery original one and I would like to know if it is possible to charge each cells independently with some device or just normal universal charger.

I Apologize if i asked in wrong section.

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So are these loose cells you have? You will require a voltage limited and current limited source to charge your li-ion batteries; something such as a lab supply will do nicely but a universal supply will probably do aswell - check its specs tho!

You'd probably want to charge the cells to a max of 4.2V (Check datasheets or go lower to be safe with 4-4.1v but you'll be storing less juice tho!). Set your current limit conservatively to c/3 or something, c is the capacity of the cells so if you had 2400mAh cells, charge them at 1/3 of that so at a rate of 800mA each. Most cells let you do 1C and few do 10C or other high charge rates but best to be safe and sure when working with these and use low currents.

If you have a whole bunch of these cells in series, you'd want to be careful because of the imbalance that may occur as Thomas pointed out. This isn't an issue with single cells however.

Also for the battery monitoring chips - they'll disconnect your battery when the voltage / current are beyond safe limits but you will still need proper charging power source as the BMS will not limit current for you.

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    \$\begingroup\$ This looks OK for the first phase of the charging cycle - the constant current phase - but once the cell voltage gets to ~4.2V (see manufacturers data sheet for the precise voltage) you have to go into constant voltage mode. When the current in this mode has dropped to a threshold value (again see data sheet) then you must switch the charging supply off. Improper charging is very dangerous. \$\endgroup\$ – uɐɪ Feb 11 '11 at 13:02
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    \$\begingroup\$ Yeah, my bad - stop your charge when your current hits around c/20. Best to MAKE SURE you stay below the 4.2V threshold tho and closer to 4.1 where possible and you should be sweet. Be fully sure they're li-ion or lipo before you charge them like this because different cells take different voltages, lifepo4 (although wouldnt be in laptop packs) does its stuff at lower voltages. \$\endgroup\$ – user2963 Feb 11 '11 at 14:18
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    \$\begingroup\$ Also be aware that some cells used old anodes which have a maximum voltage of 4.1V and nominal voltage of 3.6V. \$\endgroup\$ – Thomas O Jun 20 '11 at 22:02
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From the way that you phrased the question it sounds like you may have some cells from a disassembled battery pack. If this is the case then DO NOT TRY TO CHARGE THEM. Battery packs all contain protection electronics to prevent pack overcharging, overheating, fire and explosion. This protection is not present when you disassemble a battery pack and attempting to charge the cells is highly dangerous.

Individual cells cannot be charged with a typical NiCd or NiMH battery charger.

Any charger that you use to recharge a battery pack needs to be designed with the particular pack in mind. They all vary in terms of the number of cells in series (pack voltage) and number of batteries in parallel to give the current capacity required.

If the batteries that you have are more than a couple of years old then you may find that there storage capacity is very poor. Li-ION cells, particularly from laptops, do not have a very long life. The life of a laptop battery is particularly short as it is highly hostile to the battery chemistry. The battery does not like being fully charged and/or hot. Running your laptop from a wall charger ensures that both of these are true.

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Benchmarq/TI and Maxim make charger chips. Both are very helpful with free samples.

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You will not be able to buy an off-the-shelf charger for individual lithium-ion cells, the way you can for NiCd or NiMH rechargeable cells (AA & AAA for example). Lithium-ion requires more protection circuitry that keeps it from being overcharged (allowed to charge to too high a voltage) or overdischarged (too low a voltage) as either of those is very detrimental to the cell chemistry and may destroy its usability in one shot, certainly with repeated abuse, or even cause a fire or explosion. A pack the size of a laptop battery will also have protection against overtemperature, imbalanced cells in a multi-cell arrangement, short circuit, and so on. It may even have an encrypted code to block use of counterfeit (aftermarket) replacement packs. Removing this protection is not necessarily going to make a battery blow up, so long as it's charged and discharged in a safe way, but it will be less safe. You might want to keep it in a ventilated metal box or find some other way to make sure a firecracker-sized explosion won't hurt you if things go wrong.

If you're a hobbyist and want to run a project from a single Li-ion cell, you can do it easily enough by charging the cell on a bench power supply with BOTH current and voltage limit set appropriately for the particular chemistry. As you don't have tech specs for the cells in hand, you'd be wise to be conservative with the voltage and current limit, reducing below what Charith Perera recommended and set it around 3.8V and C/5, or 500mA for a typical laptop cell (cylinder 18mm x 65mm). That will reduce the amount of charge the battery stores, but you'll get many more cycles out of it. You can disconnect the bench supply after it goes into voltage limit mode and the cell will have most of the charge it's going to take at that voltage limit, or you can leave it a few hours more and get a little more charge into it, but don't leave it charging forever.

If you don't have a bench power supply and don't want to build your own charger circuit using standard chips from the likes of Maxim, TI, etc., then no, you probably cannot safely charge lithium-ion cells. Off the shelf chargers (like for a digital camera battery) can be designed differently from one model to another and it'd be harder to characterize their behavior than to build your own. On the other hand if you used a standard digital camera battery to power your project, then obviously it'd be fine to charge it in the associated charger. You'd still want to have a circuit in your project that turns it off when the battery voltage gets below a certain level (say 3.0V to be conservative), as overdischarging the battery will effectively destroy it. You can't discharge a rechargeable battery to zero volts the way you can with a capacitor or a disposable alkaline battery.

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I would warn against it as if you attached imbalanced cells to make a battery (each cell at a slightly different charge), you could suffer from cell failures because of polarity reversal, which, owing to the rather combustable nature of Li-ion cells, it would not be good. It is best to charge all the cells at the same time; per Leon, there are chips which do this too.

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This is not what others will want to hear but you can actually PARTIALLY charge cells safely. If ~80% charge satisfies you that is. You need a voltage controllable supply, with or without current limiting. I say without because you can add that yourself - resistor pack / bulb or whatever limits the current, preferably something that fails open not short. That being said, I bought a universal Li-Ion charger (mostly for mobile phone batteries) for 2 or 3 euros, new.

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