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

Laptop Battery : Link

  • \$\begingroup\$ 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. \$\endgroup\$ – winny Nov 23 '18 at 10:02
  • \$\begingroup\$ @winny Is there any way to calculate how much time my battery will last with the above mentioned configuration. \$\endgroup\$ – Baskaran S Nov 23 '18 at 10:05
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    \$\begingroup\$ 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. \$\endgroup\$ – Bimpelrekkie Nov 23 '18 at 10:11
  • \$\begingroup\$ 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. \$\endgroup\$ – Bimpelrekkie Nov 23 '18 at 10:19
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    \$\begingroup\$ 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. \$\endgroup\$ – Akky Nov 23 '18 at 10:19

I think that besides the 4 cells, the laptop battery also contains a controller for managing charging, discharging, etc. It also monitors the temperature of the cells and is responsible for safety in general. This is why I advise against replacing individual cells, especially with different ones. You are risking damaging your laptop or even setting it on fire and the money you will safe are not that much.

  • \$\begingroup\$ So the controller inside the battery pack doesn't cut off the power supply even if the cell exceeds a certain temperature, am I right. \$\endgroup\$ – Baskaran S Nov 23 '18 at 10:10
  • \$\begingroup\$ That depends on the design. Often the battery pack just sends an "I'm hot!" signal to the laptop to indicate that the charging should stop. The protection in the battery pack itself usually only disconnects the batteries when an over or under voltage or current is detected. \$\endgroup\$ – Bimpelrekkie Nov 23 '18 at 10:13
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    \$\begingroup\$ @Bimpelrekkie So your advice is to get a new battery pack right. \$\endgroup\$ – Baskaran S Nov 23 '18 at 10:38
  • \$\begingroup\$ If you want more endurance, then order a replacement with more cells in it. For example my Lenovo W530 laptop has a 9-cell battery pack for long on-time. It does stick out of the back, but the laptop was designed to handle it. Looking around, I don't see any options for longer endurance battery modules for the z50-70. \$\endgroup\$ – CrossRoads Nov 23 '18 at 13:58
  • \$\begingroup\$ So your advice is to get a new battery pack right. Yes it is, I came to that conclusion a long ago, replacing the cells is too much work and causes too much inconvenience, it is just not worth it. Buy a compatible battery pack which gets good reviews (look on Amazon for example). \$\endgroup\$ – Bimpelrekkie Nov 23 '18 at 14:33

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