# Factors to be considered while replacing dead cells with a new 18650 Li-Ion cell in a Laptop

I am currently using a Lenovo Z50-70 laptop. My battery condition is very poor and it lasts for only 20mins. So I decided to replace the dead cells inside the laptop battery on my own.

My Laptop battery consists of 4 cells with a Capacity of 2200mAh(14.4V). What I am planning to do is to replace all the 4 cells with a new 18650 cell with a capacity of 2600mAh of each. So my whole capacity will be (2600mAh*4=10400mAh) and each cell rated with 3.7V.

My Question is whether this going to work or not? If yes, what are the factors to be considered while replacing my dead cell with a new one? My implementation crosses the manufactures capacity, so will this going to affect my laptop in any way?

The 18650 cell I am going to use: Link

• I see no initial problems if you replace all the cells. The increace in capacity is most probably within tolerance of any BMS too. But your capacity will remain 2600 mAh since you series connect them. You don't gain voltage and capacity at the same time. – winny Nov 23 '18 at 10:02
• @winny Is there any way to calculate how much time my battery will last with the above mentioned configuration. – Baskaran S Nov 23 '18 at 10:05
• Replacing all cells with identical new cells is the way to do this. Deviate from this (not all cells, not identical, used cells) is asking for trouble and not worth it. Do use good quality cells. Buy cheap ones from ebay isn't worth it. Get cells from Samsung, Sony, LG, Sanyo or Panasonic. Yes these are more expensive but worth the money. Also consider just buying a non original but branded replacement battery (like from Patona) are often affordable and of good quality. – Bimpelrekkie Nov 23 '18 at 10:11
• So my whole capacity will be (2600mAh*4=10400mAh) No your cells are in series an that means that the capacitance stays the same at 2600 mAh. Only when you connect the cells in parallel (which you should not do!!!) is the capacity in mAh increased. If the cells are really 2600 mAh then you will get a slightly longer runtime than what your original battery had when it was new. – Bimpelrekkie Nov 23 '18 at 10:19
• Each standard battery pack (coming with laptop) or a replacement part always consists of rechargeable cells, battery management controller to charging & discharging of every cell, thermal sensor. BMS controller is factory programmed & calibrated to work with original cells. It continuously monitors for cell heath, aging, charging & discharging cycles. So even if you replace old cells with new one & with higher capacity, your BMS may not able calibrate itself again. Hence even if new cells are introduced; you may not see working time improved for your laptop. I suggest-get original replacement. – Akky Nov 23 '18 at 10:19