How to rebuild a Li-Ion battery pack

Implemented for Fujitsu - Siemens Lifebook S-Series FPCBP25 battery pack
source: Electronics-Lab.com

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Warning If you are not completely sure what you are doing, don't apply what is described below. In any case www.electronics-lab.com does not have any responsibility in any way to the consequences that this guide may have. Read it at your own risk. Please don't continue reading if you don't agree with the above.

 

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The Li-Ion battery pack we will rebuild replacing it's individual cells it's a FPCBP25 battery pack manufactured from Fujitsu - Siemens and used in Lifebook S-Series notebooks like Fujitsu-Siemens S4510, S4542, S4546, S4572 and S4576 ect. S-series of Fujitsu-Siemens notebooks are really nice so that's another reason you may don't like to replace your notebook with a new one. You may also find this pack listed with the number FMVNBP104 or CP024486-01. The nominal voltage is 10,8V and capacity is 2600mAh

The battery pack looks like in the above photo. You can read on the label the product number and the type of the battery (Li-Ion). You must also read all warnings listed and be sure to follow them, expect the disassemble one that we can't do it in another way:
 

 

It is strongly recommended not to proceed to the following operations if you are not sure what are you doing or you have not fully understand the precautions previously talked about. Continue reading with your own risk. We advice you to work in a fire safe place and take all the necessary fire safety measures.

 

Disassemble The pack is sealed to make it's disassemble hard. The cover is glued so it may be hard to remove it. Take a screwdriver and put it in the split between the two covers of the battery pack, that's beside the cover. Try to turn the screwdriver and unglue a small side. You may need to apply enough force to achieve this. Continue this operation to the entire pack. That's not too difficult, but for sure you will scratch the plastic. After some minutes you are victorious!

 

Now you have a clear view of the interior. You see that the pack comprises from 6 Li-Ion cells and a circuit board that contains all the safety circuits. After a more detailed examination you will find that the batteries and connected in three series of two batteries each one. Look at the following image to understand the actual structure. As you see the expected characteristics of each cell, according to the connection and the entire pack characteristics, are 3,6V and 1300mAh capacity.

Identifying the cells On top of each cell is a part number CGP345010 (click for the datasheet) that's a Panasonic's Li-Ion prismatic cell. As you can see in the datasheet this cell has a nominal voltage 3,7V and 1400mAh. That's above the expected value of each cell as calculated according to the battery pack characteristics, but the part number of each cell are identical (and both manufactured by Panasonic). So what's is happening? The most possible explanation is that Fujitsu has rated it's battery pack a little bit lower than the actual nominal ratings for a reason. The cell are for sure the same.

	Find the cells Now we have identified the cells that comprises the pack it's time to check if we can find them in market. Now you need to be lucky.
We found the cells on www.AllElectronics.com at a reasonable price. That's exactly the cells we need with an additional protection circuit that we don't need and we are going to remove it

Take the battery out With the help of a screwdriver lift the first battery and cut the first connector as seen on the left photo.

Lift carefully the second cell trying not to damage the circuit board.

With the help of a cutter, cut the remaining metallic contact and keep it as you will need it later.

Now cut the other side of the contact that goes to the pcb.

Continue cutting the other edge of the contact.

Continue removing the next cells in series.

In the final cell you must pay more attention because there is a PTC attached on top of it. Carefully remove the adhesive tape and free it from the cell. Now you can also remove this cell.

Place all cells in a distance so there is no chance to short circuit them. Don't throw away old ones as you will need them later.

Finally remove carefully the safety circuit board without damaging it, as we will use it again!

 

 

 

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