Keywords：LiFePO4 series-parallel, lithium battery configuration, ESS design

Many systems require both higher voltage and higher capacity, leading to mixed series–parallel configurations.

1. Balanced Design Is Critical

Each parallel group must be well balanced before being connected in series.
Otherwise:

• The weakest parallel group limits the entire series string
• Voltage drift increases
• BMS balancing stress rises

2. Impact on Charging and Discharging Efficiency

Series–parallel systems often face:

• Uneven current distribution
• Uneven temperature rise
• Higher BMS workload

This directly influences how efficiently the pack delivers energy.

3. More Complex BMS Requirements

In mixed configurations, the BMS must manage:

• Multiple balancing layers
• Parallel group supervision
• Serial group protection thresholds

Advanced BMS with cell monitoring and CAN/RS485 communication is recommended.

4. Scalability for Large ESS

Series–parallel architecture is widely used in:

• 51.2V rack-mounted batteries
• 100Ah / 200Ah ESS cabinets
• Containerized battery energy storage systems

It allows flexible combinations to reach kWh to MWh level.