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Currently I am looking for eight new 18650 battery cells to rebuild my iBook G4 (A1055) battery pack. Because I can't find for what discharge rate the original cells are rated, I'm not sure which cells to pick. The original cells are Panasonic CGR18650CA (datasheet is for a slightly different type, I know), but in the datasheet is not specifically described what the maximum discharge rate can be. There is a mention of actual capacity vs discharge rate, the highest being 4080mA given as an example. Is there a general 'safe' rating for laptop battery pack cells?

The cell type I am planning to buy is the Samsung ICR18650-26H. This cell can have a discharge rate of 5200mA.

Here is a schematic of the cells as connected in the iBook G4 battery:

schematic

simulate this circuit – Schematic created using CircuitLab

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    \$\begingroup\$ What is the capacity and how long does the battery last (when new). Average discharge rate is capacity / battery life. \$\endgroup\$
    – user57037
    Commented Jul 24, 2016 at 20:28
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    \$\begingroup\$ Thank you! The capacity is 61Wh @ 14.4V = 4236.1mAh or 4.2361Ah. The battery life as stated by Apple is 6 hours. That would make the discharge rate 706mA or 0.706A. This would mean the usage is well below the rating of the Samsung cell. The battery pack has some cells connected in series and others in parallel. Does this have any effect on the discharge rate per cell? \$\endgroup\$
    – Luchador95
    Commented Jul 24, 2016 at 20:58
  • \$\begingroup\$ No, that number is the discharge rate and you will be had pressed to find an 18650 which can't support that current. \$\endgroup\$
    – winny
    Commented Jul 24, 2016 at 22:55
  • \$\begingroup\$ Average discharge rate has nothing to do with the peak discharge rate, which is what you are after. If you have some decent instrumentation and a bench power supply you can measure the peak current consumption, add some safety margin and start from there. 0.7A for a 4Ah battery is ridiculously low, a modern 4Ah battery can easily provide 10A. \$\endgroup\$
    – Vladimir Cravero
    Commented Jul 24, 2016 at 23:21
  • \$\begingroup\$ How many cells total are there? Since it is 14.4V, that means the series voltage is equivalent to 4 cells in series. I am guessing the number is a multiple of 4. Maybe 8? So it is 4 series, 2 parallel (4s2p). Is that correct? \$\endgroup\$
    – user57037
    Commented Jul 25, 2016 at 2:22

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Ask yourself this, can I remove the battery from the laptop and still have it run fine if it is plugged in? I am assuming this is a yes. This would mean that the load is being met by the supply from your battery charger. So, so long as you have the same continuous current capacity from your battery pack that you do from your charger you should be set.

If we assume that that rate is less than 5amps, (you have a pig of a laptop if it is that much) then you are golden as almost all genuine 18650 cells can source at least that much. Many source up to 15-30amps even.

You are also asking if it is safe to have too high of a discharge capability of your cells: No, not really. If you draw only 5amps out of a cell that can source 30, that is fine. The cells will always run a cooler than if you were taxing it more. So that is good.

If you want a bit more help, I would recommend the sanyo ncr 18650 ga cell. It can source up to 10amps continuously. You only need <5amps so it will run nice and cool. It also has one of the highest capacities of all the 18650 cells available these days so your battery will last nice and long between charges.

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