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I accidentally broke down the charge controller on my new Powerbank.

However I am left with a brand new unused 20.000 mAh Li-ion Battery. Which I was planning to hookup to a new charging module/powerbank circuit.

But then I saw the writing on the battery and Googled it, but couldn't find a lot of useful information.

Writing is: 3.85/4.4V.

I personally never have seen a battery above 4.25 V

So I have a few questions:

  1. What's the safe cutoff low voltage on this battery?

  2. Due to the differences in voltage, can I still hook up this battery to standard powerbank circuit?

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  • \$\begingroup\$ Most common are 4.2/4.25, but there are 4.3 options and even 4.4V. Of course, you can use it with 4.2V controller, but you'll lose some capacity, hard to say how much, maybe even 15%, depends on discharge curve, it may have a lot of energy between 4.4 and 4.2. Cutoff depends on controller too, the cell itself can discharge even down to zero, but the controllers decide when to consider it empty. Usually 3.0V or so, sometimes 3.2V, sometimes even 2.8V. At that voltage there is already little energy left, like a few drops on the bottom of the bottle. I wouldn't care about bottom limit much. \$\endgroup\$
    – Ilya
    Commented Sep 3, 2020 at 14:56
  • \$\begingroup\$ I'm not 100% expert, I would wait for some smart people to comment first :) \$\endgroup\$
    – Ilya
    Commented Sep 3, 2020 at 14:56

2 Answers 2

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  1. The cutoff voltage is 4.4 V. It's a high voltage lithium polymer accumulator.

  2. You can hook it up to a standard charging circuit (that means 4.2 V cutoff I assume) but you won't get the claimed capacity out of it. But you will drastically increase the cycle count of the battery, so that's a plus.

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  • \$\begingroup\$ Well it depends if you would like to have the same level cut off as before to avoid deep discharge \$\endgroup\$
    – user103776
    Commented Sep 2, 2020 at 15:21
  • \$\begingroup\$ @AntonIngemarson I don't quite get your comment - both normal LiPo and high voltage LiPo can be discharged to 3 V, so no worries with overdischarging with a normal protection circuit. Or is my research in that direction incorrect? \$\endgroup\$
    – Arsenal
    Commented Sep 2, 2020 at 15:25
  • \$\begingroup\$ batteryuniversity.com/learn/article/discharge_methods " Depth of Discharge Lead acid discharges to 1.75V/cell; nickel-based system to 1.0V/cell; and most Li-ion to 3.0V/cell. " I also have a memory of that it differs when I last looked at litium battieries types. \$\endgroup\$
    – user103776
    Commented Sep 2, 2020 at 15:30
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The battery industry raised the voltage a few years back from a maximum of 4.2 V to the present-day value of 4.35 V. This was responsible for adding approximately 4 to 5% to the energy density. A new crop of batteries is now beginning to operate at 4.4 V, adding an additional 4 to 5% to the energy density. But that does not come without some serious challenges.

What are they?

  • Higher E-field forces demand better Lithium-Cobalt-Oxygen chemistries.

  • Depletion of Lithium ions towards anode during CV mode must not exceed 50%. these are considerations for a battery engineer to choose the best tradeoff between rapid charge time , capacity and reasonable charge life which are all tradeoffs.

  • The result is higher energy density but the risk of OV damage and OC destructive damage during the region above 3.85V , which may be used as the threshold to recycle charger.

ESR and C charge ratios for current need to be reduced above this threshold so you might research the optimum CC1, CC2, CV and cutoff thresholds or use conservative standard 4.2V limits.

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