Solving battery pack self-discharge

Batteries and Chargers Rechargeable Batteries
1

I have few batteries packs which lose about 0.5v per day. And I want to fix this issue.
The pack have 220v connection for charging that goes directly to the wall outlet and two output terminals for ~DC 8V.
I have opened the pack and inside it there:

  1. A single PCB (probably only for AC to DC convert and charging management)
  2. 2S1P pack with an internal BMS

When I have disconnected the pack from the PCB it kept the voltage, so I assume thar the leakage is from the main PCB.
At first try I have added a switch to disconnect the battery from the PCB while it is not in charging/usage, but it needs to be switched manually so I am looking for better solution.

I have thought to:

  1. Add a diode on the positive connection between the pack to the PCB to only allow charging but not discharging
  2. Connect the output terminals directly to the Pack (after the BMS) as alternative output for using the battery.

Changes to the original circuit are in red pen.
What are your thoughts?

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2

A diode will steal 0,25-0,3 volts and your battery won’t get fully charged.
If there’s enough room you can use an “ideal diode” which looses only 50-60 mV. But make sure to order a dual pole module like this
image

since single pole modules don’t work well in charging circuits.
image

3

Thank you for this answer.

just to clarify:
Singl pole is like a standard Diode with in and out while dual pole also connected to GND (aka the minus of the battery) ?

4

Yes

Yes, minus of the charger and the battery.

1 Thank