It depends on what you need. But you should start by looking at Keithley's SourceMeter "source measure units" and competing instruments from Keysight and Rohde

It depends on what you need. But you should start by looking at Keithley's SourceMeter "source measure units" and competing instruments from Keysight and Rohde & Schwartz. There are even specific instruments in this vein that can emulate battery charge/discharge models out of the box. These are typically called "battery simulators" or "battery emulators". https://www.tek.com/en/products/keithley/dc-power-supplies/2281s-series-battery-simulator-emulator https://www.tek.com/en/products/keithley/dc-power-supplies/2... https://www.keysight.com/us/en/product/E36731A/battery-emulator-and-profiler.html https://www.keysight.com/us/en/product/E36731A/battery-emula...