Recently I refreshed a laptop battery with new 18650's. This is working however it still doesn't last very long because of the chip inside this battery.

The chip must recalibrated (data is incorrect and based upon previous batteries) but cannot do this. There are smart chargers that can charge 18650 without any problem and can determine the condition of the cell as well. So why is the charge circuit inside the battery and not inside the device? The circuitry/chip inside the battery makes the whole battery pack unusable.

The batteries I have replaced seems to be working fine after a full recharge later in an external charger. Test for several days and operate just fine with different loads. So the chip inside the battery pack decides the battery is dead at some circumstances but in fact it's not.

18650 is a standard, so why do manufacturers decide to design custom packages of a standard? In the early days, you replaced batteries by purchasing "dumb" /unprotected (single use or rechargeable) cells. Easy as 1,2,3, widely available, old out - new in, easy. Nowadays you need to buy an expensive customized battery pack for some reason, even when using an industry standard inside.

As an example, the batteries I replaced inside this battery, is actually very straightforward. The batteries are aligned/arranged in three columns (series) of two batteries (parallel) each, like this:

battery arrangement

This could be easily a battery compartment with six 18650 'slots' without more space requirement and when the charger is available in device, also without charge circuitry. Reusable (avoid electronic waste), overall a much cheaper solution or not?

So why do manufacturers still design custom battery packages instead of an industry standard? What's the real reason?

Is it because of (some ideas):

  1. Safety, because of possible shorts by wrong polarity of unprotected cells;
  2. Avoid unpredictable results of the product by using low quality batteries*;
  3. Dependency, you need to buy original (overpriced) customized battery pack;
  4. Sales, control failure and replacement (like ink cartridges, black gold);
  5. Product life cycle, product become obsolete when no battery available

*= Counterfeit batteries and low quality batteries, in my opinion, caused by the exclusivity and high prices of the brands themselves. Bad batteries are around us for decades so this could not be a real excuse. A warning in the manual to use good quality batteries is enough to avoid claims.


  • 2
    \$\begingroup\$ To sell parts. A few batteries in a battery slice can run well in excess of 100$. But it’s just a chip, a bit of circuitry and some batteries:/ You can usually see the design capacity, last-full capacity and current capacity in Ah using upower -d on GNU/Linux, as reported by the system. I’ve had the same problem as you, though it seemed to go away after swapping slices both when on AC power, hard-off, and during reboots. What is the brand and model of laptop? \$\endgroup\$
    – user2497
    Dec 25, 2017 at 21:13
  • \$\begingroup\$ Hi thanks for the answer. I don't understand "swapping slices both when on AC power, hard-off, and during reboots", what do you mean with swapping slices? It's a Fijutsu-Siemens, an older model, the L1300. Still in nice condition. Inside the battery pack there where Panasonic CGH18650C cells, qood quality cells. The battery starts to mallfunction after a longer period of no use. \$\endgroup\$
    – Codebeat
    Dec 25, 2017 at 21:23
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    \$\begingroup\$ The target customer doesn't think on the level of 18650 cells \$\endgroup\$
    – PlasmaHH
    Dec 25, 2017 at 22:21
  • 2
    \$\begingroup\$ Thinking back to before Li cells, (e.g. NiCd, NiMH), you still had proprietary packs. If there weren't provisions for primary batteries, usually there was a pack. And most of those were "dumb" packs as well. \$\endgroup\$
    – W5VO
    Dec 26, 2017 at 0:34
  • 1
    \$\begingroup\$ @W5VO Yes, that’d be an interesting solution. Nothing should prevent a user from replacing his cells manually. \$\endgroup\$
    – user2497
    Dec 26, 2017 at 18:45

2 Answers 2


Is it because of (some ideas):

Safety, because of possible shorts by wrong polarity of unprotected cells;

Sure, that's the main reason. A Li-Ion cell isn't consumer-friendly, as it may explode into your face when shorted or put into a pack with wrong polarity. It needs a protection against those cases.

Avoid unpredictable results of the product by using low quality batteries*; Dependancy, you need to buy original (overpriced) customized battery pack; Sales, control failure and replacement (like ink cardridges, black gold); Product life cycle, product become obsolete when no battery available

This doesn't even work for ink cartridges.

  • \$\begingroup\$ Thanks for the answer, expected this answer. However, if you use protected cells instead, this doesn't have to be an issue, right? And if you use protected cells (slightly larger), unprotected cells won't fit. I think this will be much safer than one protection for all cells like used in the battery pack. When something happen between those cells, a short for example, the protection doesn't make any sense, battery may still explode. For sure, current solution is better than nothing and maybe cheaper but I still not convinced this is the real reason. \$\endgroup\$
    – Codebeat
    Dec 25, 2017 at 23:49
  • \$\begingroup\$ The protected cells have the charge controller IC built-in, this is a feasible solution, but charge controller ICs for battery packs often have distinct pins for each inter-cell connection. Take a look at the LTC6801 or the MAX11081. \$\endgroup\$
    – Janka
    Dec 26, 2017 at 0:48
  • \$\begingroup\$ I'm not sure what you mean with "charge controller IC built-in". The protected cells have a protection ic that protects the cell from overcharge, overdischarge, overcurrent. This protection ic has nothing to do with the overall charge process of an array of cells (monitoring, balancing etc), it is only there to protect the individual cell which is good. I don't understand why manufacturers sell unprotected cells anyway because it could be dangerous. \$\endgroup\$
    – Codebeat
    Dec 26, 2017 at 11:51

Internal Pack BMS chips offer many advantages

  • individual cell health monitoring and optimal control for temperature, SoC or DoD, charge rate settings for CC, CV and cutoff vs cell T.
    • safety, maximum cell life, reliability, lower cost, higher value
      • over current protection (OCP) during charge and discharge
      • under/over temperature protection (UTP/OTP) during charge, discharge or not in use
      • under/over voltage protection (UVP/OVP) during charge and discharge
      • pre-charge, fast-charge timeout protection in flash data
  • disadvantage is incorrect historical data may indicate false flag protection on new cells unless correct recal. commands are used

Example State-of-the-Art TI BMS chip with SM Bus interface for laptop.

enter image description here

note: This chip has support for 4 cells for temp sensing, voltage monitoring, and AFE fusing, which is more costly by external methods.

My impressions

Internal smart charge controllers with active balancers and shunt circuit failure protection, offer extended capacity, longevity, performance value and of greatest importance, safety from overcharging a reduced capacity cell. By balancing state of charge for each cell during charge and discharge is the ideal way to maximize the lifetime capacity of any array.

It could be designed either way, but it would be better calibrated as a package since there are imbalance limits to power dissipation for balancers and the rate of aging accelerates rapidly from any imbalance resulting in over/under-charge.

Some people keep the SoC between 25% and 90% to prevent this risk and simply cycle batteries more often with a balanced charger. I recall the Lenova Laptop charger used an algorithm like this to maintain SoC around 50% while plugged in for extended periods. This SoC level reduces the aging rate and is used for shipping storage as well.

Further reading, other options http://www.electricrcaircraftguy.com/2013/01/parallel-charging-your-lipo-batteries_22.html

  • \$\begingroup\$ Thanks for the documentation however this is not an answer to my question. \$\endgroup\$
    – Codebeat
    Dec 26, 2017 at 12:06
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    \$\begingroup\$ The implied reason is that internal contructed BMS chips are superior along with bin matching each cell. If one simply swaps out cells with 10% tolerance on mAh, then pack life is actually much worse than life of weakest cell, because it is also stressed the most from over/under/charge voltage unless internally monitored and balanced. Also those selected for internal smart controllers always carefully binned for matching mAh and ESR. \$\endgroup\$ Dec 26, 2017 at 18:52
  • \$\begingroup\$ Battery models are just as complex as semiconductors, so a thorough discussion requires that you understand the EIS chemical model and all the related terms. Simply swapping out cells with matching or BMS balancer is foolhardy without detection and internal safety design from short circuit faults. \$\endgroup\$ Dec 26, 2017 at 19:09

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