since there is no longer good source of high quality pouch flat type Li ion cells, I am considering to use high new smartphone batteries from service packs.

I need bigger capacity - about 10 - 20 Ah, so using 4Ah cells I am on 3 -5 cells in parallel. I am using single cell scenario - 3S1P or 5S1P.

Are there any drawback in charging all these cells in parallel with original PCM? I know that PCM will disconnect each battery randomly during charge and discharge. It seems that during charge I need charger with 4 A charge current max to fully protect case that only one cell`s PCB is allowing to charge.

Am I missing something?

P.S.: I dont want to remove PCMs from these pouch type batteries, soldering can be quite tricky and dangerous on these soft plastic packages...

  • \$\begingroup\$ Consider adding a SMALL resistance in series with each cell (wiring may be enough) to ensure that worst case IR drops are smaller than the drops in the wiring. This is an inexact art . Losses can usually be small. \$\endgroup\$
    – Russell McMahon
    Sep 13, 2019 at 9:19

1 Answer 1


As always, it depends. How closely matched are the capacities and internal resistance of the batteries in parallel and how much current will you push? If very little compared to capacity then most likely no problem. A lot of current and big mismatch in capacity and internal resistance then the following will happen:

(Image stolen from Wolf at secondlifestorage.com, but I'm sure he won't mind) enter image description here

Link to thread: https://secondlifestorage.com/showthread.php?tid=7873

I know that PCM will disconnect each battery randomly during charge and discharge

Sounds like the BMS (you call them PCM?) is protecting the cells from this very event. If you lower the current, does this stop?

Am I missing something?

How does the charger/overall system react to the BMS/PCM tripping in rapid succession?

  • \$\begingroup\$ I would like to pull 6A from 4Ah cells. 1 cell could handle it, but I need long term reliable battery so 2 or 3 batteries in parallel would be much better. Capacities and ESR of batteries should match very closely to factory standarts. I am talking about brand new (Samsung or Sony ) cells, purchased in big batches. Yes PCM is almost same as BMS :) I usually use term BMS (Management) for protection with SMbus or other MCU interface. Charger of course had some issues, some circuits (more advanced) were complaining and evoked error. 220 uF output capacitor seems to eliminate this issue. \$\endgroup\$
    – HeliTux
    Sep 13, 2019 at 9:14

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