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DIY re-celling laptop battery

March 7th, 2016

I have a Sony VAIO VGN-SR59 laptop, which batteries capacity significantly dropped from ageing 🙁 This laptop is already something like six years old. From the economical point, it is not worth to buy a new genuine Sony battery anymore because they are quite expensive. However the laptop runs still reasonable well for its age. But what are other options?

Buying non-genuine laptop’s battery

Whatever brand is your laptop (Sony, HP, Mac) but both eBay and Amazon are flooded by non-genuine batteries. They are pretty cheap compared to original batteries but are they good? I decided to try and get one non-branded Li-Ion VGP-BPS13A battery for my Sony laptop.

Re-celling laptop battery Noname brand

The official vendors try in different ways to prevent the users from using non-genuine batteries. For instance, Sony even released the bios update which target exactly this and it does not allow to charge non-genuine battery 😉 If you consider to get such battery from eBay, just pay attention to the description of the battery. It should clearly say that non-original battery will work with your Windows XYZ version, opposite you might be in trouble.

But the guys from Asia managed to crack even such limitations in some cases. As a result, my bought non-branded battery from eBay was detected and worked pretty well under Windows 7.

Non-genuine batteries performance and issues

So far so good. But the VGP-BPS13A battery lasted not for long, for some good ~4-5 months and its capacity significantly dropped again. Not good 🙁

So, I decided to perform a surgery and I opened the battery. To do this, I started to deform the battery bit by bit in my hands by forcing the cover in opposite directions. As it appeared later,  that was not very difficult because there were only few glued places of the cover parts.
After ~10 min, it was already open 🙂 and it appeared that the battery was assembled from green colour OEM Li-Ion cells with no manufacturer on them with marked capacity of 1800 mAh. Two cells were connected in parallel and each 2-cell was placed in 3x series. All that would give 3600 mAh capacity for your laptop. That is pretty common configuration of the laptop’s battery.

I was curious to assess their conditions and I decided to measure their internal resistance. There is pretty simple trick to do so.

Re-celling laptop battery Rheostat

Procedure of assessing internal resistance

First, you have to charge the battery fully and measure cell’s (not the batteries pack!) voltage v1. Next, load the cell with the linear load (high wattage resistor or rheostat) R, let’s say 1A current. That’s should be safe, as it would be only 55% of labeled capacity (each cell is 1800mAh in my case). To do that, I managed to find an ancient rheostat as a load R.
If you can’t find such, you might buy a 5W 6 ohms resistor from eBay. That should produce a 0.7A current from the cell and some voltage drop on the cell too. Let’s measure another voltage V2 under this load.
At this point, you should know the load resistance R, and two voltages with no load v1 and with the load V2 🙂 After all that you have just use this equation to calculate whatever type battery’s internal resistance r:

r=(V1 x R)/V2-R.

Here are the results of my non-branded battery cells:

#1 – 131 mΩ
#2 – 178 mΩ
#3 – 131 mΩ
#4 – 132 mΩ

As an example, Sanyo provides the internal resistance in the datasheet for its UR18500FK  less than 100 mΩ. As you could see all measured internal resistance values are above compared to Sanyo dataheet’s specs.

DIY re-celling

The last third alternative is to do DIY re-celling of your laptop battery 😉 I ended up with this approach by re-celling non-branded battery from eBay.

Re-celling laptop battery

First just get some established brands like LG, Panasonic, Sanyo or Sony UR1850 size batteries either from eBay or some other shop.

Pay attention what is the current capacity of the cells! The reason is that the battery capacity and other parameters are programmed into the charging controller inside the battery pack. So, if you will fit different capacity cells inside the battery pack the parameters like the charging/discharging currents and other will remain unchanged. The result of this is that the prediction of how much of the battery is remaining can become unreliable.

However, it might be that it is either to complex or too expensive is to get the same capacity cells. Then it might be acceptable that you will lose the accuracy of the predictions for the battery pack.

Couple last things

Once you will start to replace the cells, try to not overheat them as well. Some of the cells are equipped with overheating protection 😉

There are cases, in which the re-celled battery does not accept charging. For some people, it helped to apply 12v DC voltage to unblock the charging controller. Some other used this procedure to restore the charging. In my case, I tried both but none of them helped me, so I just left battery inside the laptop plugged to the charger and it started to charge after ~30 min 🙂

And of course, you have to recalibrate your battery pack to enjoy your freshly re-celled battery. You can do this by fully discharging the battery and fully charging it. I used just a live USB Linux distribution to fully drain the battery. In some case, you might have to do it two or three times. After doing this, do not drain your battery up to 0%, as e.g. lithium-ion batteries hate that and degrade pretty quickly if you are doing that to often.