Fox ESS ECS4000 Battery CS4000 | Slave battery module | Capacity 3.975kWhThe CS4000 is a LiFePO (lithium iron phosphate) battery slave module within the ECS4000 series. It pairs with a CM4000 controller module to form scalable battery stackseach CS4000 adds ~3. 97 kWh of capacity. Key Features High Voltage, High Performance: Enables scalable stacks up to ~459. 9 V Plug and Play Design: Snap fit modules with CAN bus communication simplify installation Safety & Certifications: UL1973, UL9540, UL9540A, UN38. 3 certified;