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I am designing a PCB which has 4x Primary Lithium cell Batteries (ER14505M) two in series and two in parallel to give 7.2 V 4400 mAh. The cells have their own holder so it would be possible to only one of the four in the wrong way.

I've done some research around it and I think that I need to have a schottky in series with each cell to prevent one cell charging another in parallel. (The voltage drop isn't a concern.)

My confusion is around having the diode + resistor in parallel. Resistor would be there to limit the current through the diode. My original thoughts were that this would protect against reverse polarity but now I'm thinking that it would only protect if both cells in parallel were the wrong way.

My question is, how do I add protection to a 2S2P Configuration (if all cells can be inserted individually) to prevent one cell charging another if one cell is flat or if a cell is inserted the wrong way?

Battery Holder

My 2S2P Configuration

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One diode in series with each battery is all you need. The diode and resistor in series do nothing, as the other two diodes prevent current from flowing in that direction, regardless of the orientation of the battery.

Of course, you lose power to a diode from its forward voltage, even if the forward voltage is as low as 0.3V, that's still 0.3/7.2 = 4% of your power being lost, so you might want to look at using a MOSFET, or some kind of mechanical protection against reverse polarity.

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  • \$\begingroup\$ Thanks, I’m unable to see how I could use a mosfet/s with this configuration of series and parallel cells \$\endgroup\$
    – Mike
    Commented Nov 18, 2023 at 22:08

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