For a while there's been one question in my head to which i could not find a solid, definitive answer no matter where i searched for so I decided to find the answer myself and also post it here in case anyone wants to use the circuitry from laptop battery packs.
The question i'm talking about is basically "how are they charged and what does the circuit do ?".
The quick answer is that the circuitry does over/under voltage protection, over heat protection, charge management, battery pack anayzing, cell balancing and over/under current protection, which are alot of great features that you can get basically for free.
I decided to rig a couple of wires to a pack and pop it into my laptop to see what it does.
Basically the laptop does the CV/CC charging while the battery pack circuitry balances and protects, simple anough.
So to charge the battery, depending on what battery you have, you plug a CV/CC power supply to the + and - terminals.
For example a 11.1V laptop battery has 3 cells ( 11.1V / 3.7V = 3S ) so the charge voltage will be 12.6V ( 4.2V * 3S = 12.6 V ).
The current will be the battery capacity multiplied by 0.5C . For example 4400mAh * 0.5C = 2200mA maximum charge current.
CV/CC ( constant voltage/current ) PSU is absolutely necessary because that's how Li-XX cells are charged, luckily they can be found on eBay for cheap.
http://www.ebay.com/itm/7-35V-to-1-25-30V-Step-down-CC-CV-Power-Supply-Module-Converter-LED-driver-New-/351328646847?hash=item51ccd1b6bf:g:nZAAAOSwBLlU8V0rThe converter linked above can be used to charge the laptop battery from a laptop PSU, or any PSU that has a voltage at least 2V higher than the required charge voltage.
Laptop PSU
can not be used to charge the laptop battery
directly !!! Or else it
will damage the battery.
I hope this helps and thanks for reading.