Li-Ion battery discharge station

Main project requirements and background

Li-Ion battery testing process: The procedure includes several steps: measuring internal resistance, assessing voltage drop under load, and determining battery capacity. The battery is fully charged, then a 1A load test is performed 24 hours later. In this project, I use the following criterion for batteries with a capacity of 1500-4000mAh: under a 1A load, the voltage should not immediately drop below 4V. If it does, the battery is rejected. Batteries that pass this stage are discharged to 3V with an electronic load to measure capacity. Measuring internal resistance also helps identify defective batteries before charge/discharge cycling.
Safe handling of rejected batteries: Rejected batteries still contain residual energy. Damage or a short circuit can cause overheating and fire. Before taking them to a specialized collection or recycling facility, insulate the terminals with non-conductive tape or place each battery in a separate bag, and protect the batteries from damage. In this project, residual energy is additionally removed by controlled discharge.
Purpose of the discharge station:
- Capture and use the batteries' remaining energy.
- Perform a controlled deep discharge to reduce residual energy before the batteries are sent for specialized recycling.

The discharge station consists of two independent compartments with separate terminals on opposite sides of the housing.

Energy Extraction Compartment: This compartment discharges a battery in a controlled manner, allowing the remaining energy to be used. It includes reverse-polarity protection based on an ideal diode; battery voltage can be monitored with a voltmeter.
Deep Discharge Compartment: Intended for controlled deep discharge of rejected batteries before recycling. Six resistors connected in parallel serve as the load, and an LED indicates that discharge is in progress.

The following key components are shown and numbered in the first photo above:

12mm momentary metal push button - used to turn on the voltmeter.
BMS 1S 10A - prevents over-discharge in the energy extraction compartment, protecting usable cells from excessive discharge.
XL74610 module - acts as an ideal diode and protects the device from reverse-polarity connections. The module is rated for up to 15A without a heatsink at 12V and 25°C in a 30-minute test. Conventional silicon and Schottky diodes are less suitable here because of their higher voltage drop. As an alternative to the ideal diode, you can use the protection circuit described here.
2-wire 0.28in voltmeter - displays battery voltage and is turned on by pressing the button.
USB boost module TPS61088 (input 2.8-4.5V) - supports QC 2.0/3.0, FCP, and AFC; it is also detected as DCP. Maximum output power is up to 24W (5V/3A, 9V/2A, 12V/2A). Heatsinks are installed on the module to improve cooling.
3mm green LED - indicates that deep discharge is in progress.
100Ohm 0.25W resistor (Amazon) (AliExpress) - protects the LED and limits its brightness. To change the brightness, select a different resistor value.
6 parallel-connected 51Ohm 10W resistors - the nominal equivalent resistance is 8.5Ohm. At about 3.4V, the current is approximately 400mA; the current decreases as the battery discharges.

The device is housed in a transparent plastic box, commonly used for office supplies.

Optionally, a USB wattmeter such as the HiDANCE HDC-085C can be used to monitor power, voltage, and current at the USB output.