laptop battery cells measurement [closed]

Question

I have two dell laptop Li-on batteries (J1KDN, 11.1 V Capacity 48Wh, Min 4.2a). One battery seems to loose its charge very fast and the second one just turns turns off around 70% (with no warning).

Before disposing them I was thinking that I might be able to create one of them by combining the individual cells that are still good from both batteries.

Each battery consists of 6 cells and each cell has 3.6 V , I have tested one of the batteries from the two connector terminals and it gave me 11.4 V (higher than the 11.1 on the label).

So the question is how can I test each cell and verify which one is a keeper or not? and number two can I do that using only my multimeter or I also need additional equipment and what is it if any?

(The way that I was thinking of doing it was just checking for each cell if it is between 3.0-3.6 V but I am thinking that this is very simple to be the correct and only way).

Answer 1

What you are thinking of doing has been done successfully a lot of times. FIRST, read the answer above carefully, if you do not understand the li-ion batteries, do not do this, but if you are ok with li-ion then it can be done quite easily if you have the right tools.

Most people will very carefully dissamble both laptop batteries, being careful not to destroy the battery management system.

Measure each individual cell's voltage, if any cell is less than 3 volts, it is no good and don't use it. Any cell that is greater than 3 volts, is likely ok. This is where having the right tools is nice. If you have a fancy li-ion charger/discharger, you would then charge all of the "good" cells fully and then discharge then and measure their capacity. Take all of the cells with the same capacity and put them together the way you found them to make one laptop battery.

Another way is to fully charge both laptop batteries, then fully disassemble them carefully. Find something electric like a toy or LED lightbulb that you can use to connect a cell to discharge it and time the discharge.(Be careful to measure the voltage of the cell periodically to make sure that it doesn't below 3.0 volts when doing this). The cells that took the same time to discharge will be of the same capacity and ideal for rebuilding into the one laptop battery. The bad cells from each of the laptop batteries will likely discharge very quickly or almost immediately, so it should be easy to find the bad cells in each of the laptop batteries and discard them.

Be careful when rebuilding the laptop battery that all the connectings are the same as when you disassembled it.

If you do it right you will save yourself from buying a new laptop battery! good luck!

Answer 2

Athanatos,

Take my advice and don't mess around with Lithium Ion Cells. They are very dangerous for a number of reasons.

There are safety devices built into these batteries which prevent a host of disasters from occuring during use and during charging. These safety devices are there for a good reason.