When working with batteries, having a power supply which can both sink and source current to simulate a battery is extremely useful. Batteries take a long time to charge and discharge and can be dangerous if you are testing features of a BMS which are not robust yet.
Commercial options like the Keithley SMUs are extremely expensive, and can be overkill for many tests.

The design is intended for single cell battery simulation, or for any general purpose supply needed for sink/source up to approximately 3A and up to 4.7V. The main IC used for this design is the OPA569 power amplifier, which has a low voltage range up to 5.5V and up to 2A sink/source capability. The output voltage is controlled using a potentiometer.

Due to the higher power dissipation, I decided to experiment with a few different options to control the fan speed. One option utilizes a comparator (TLV3201) to trip once a thermistor indicates the temperature is too high. The other option is to use a Schmitt trigger with adjustable PWM in order to have a variable speed fan that remains on all the time. In reality only the comparator with thermistor is really needed, and ended up working well in the final design.