Introduction

A LiFePO4 battery installation is not complete when the last cable has been connected.

Before the system is released for normal operation, the installer should verify:

• Mechanical installation
• Electrical polarity
• Battery and string voltage
• Cable and protection ratings
• BMS communication
• Inverter settings
• Charging behaviour
• Discharging behaviour
• Current sharing
• Connection temperature
• Alarm and shutdown functions

This process is known as commissioning.

A structured commissioning procedure helps identify installation errors before they become repeated BMS alarms, overheating, reduced usable capacity or customer complaints.

This guide is designed for rack-mounted batteries, wall-mounted batteries, floor-standing ESS units and other modular LiFePO4 energy storage systems connected in series, parallel or series-parallel configurations.

Why Commissioning Is Especially Important for Multi-Battery Banks

A single battery installation has relatively few connection points.

A multi-battery bank may include:

• Multiple battery modules
• Several branch fuses
• Positive and negative busbars
• Series interconnection cables
• Main DC cables
• Communication cables
• Master-slave addresses
• Inverter communication
• External contactors
• Pre-charge circuits
• Emergency disconnects

Every additional battery and connection creates another possible source of resistance, polarity error, communication conflict or uneven current sharing.

In series installations, voltage differences between batteries may cause one battery to reach its charge or discharge limit before the others.

In parallel installations, resistance differences may cause one battery to carry more current.

In series-parallel installations, both conditions must be evaluated.

Stage 1: Review the Approved System Design

Before energising the system, compare the completed installation with the approved drawing and bill of materials.

Confirm:

• Battery model and quantity
• Nominal battery voltage
• Required series quantity
• Required parallel quantity
• Total nominal energy
• Inverter DC operating range
• Maximum charging current
• Maximum discharge current
• BMS communication protocol
• Cable sizes
• Fuse and breaker ratings
• Busbar ratings
• Grounding arrangement
• Emergency isolation method

Do not continue when the installed configuration differs from the approved design.

A common example is replacing one battery model with another that has the same nominal voltage but a different BMS current limit or communication firmware.

Stage 2: Confirm Series and Parallel Compatibility

Not every LiFePO4 battery can be externally connected in series.

Before commissioning a series bank, confirm:

• Series operation is permitted
• Maximum series quantity
• Maximum total bank voltage
• BMS behaviour in series
• Charging requirements
• Communication limitations
• Required external protection

Series connection limits are model-specific and must be taken from the product manual or supplier.

For parallel installations, confirm:

• Maximum parallel quantity
• Required firmware version
• Address range
• Master-slave configuration
• Compatible battery capacities
• Approved communication cable arrangement

For series-parallel installations, every parallel string must contain the same number and model of batteries.

Stage 3: Mechanical Inspection

Before electrical testing, inspect the physical installation.

Battery Position

Verify that each battery is:

• Securely mounted
• Correctly oriented
• Protected against movement
• Accessible for maintenance
• Installed with the required ventilation clearance
• Protected from water, condensation and excessive dust

Cable Routing

Check that battery cables:

• Are supported correctly
• Do not rub against sharp metal edges
• Are not under mechanical tension
• Have an appropriate bend radius
• Are separated from hot surfaces
• Do not obstruct ventilation
• Are clearly labelled

Terminal Inspection

Check:

• Correct lug size
• Correct washer arrangement
• Clean contact surfaces
• No paint or insulation trapped in the contact area
• No twisted cable stress on terminals
• Terminal bolts tightened to the manufacturer’s specified torque
• Protective terminal covers installed

Do not apply a generic torque value to every battery. Terminal structure, thread size and material vary between products.

Record the actual torque value used for each connection type.

Stage 4: Polarity and Continuity Verification

Reverse polarity can damage the inverter, BMS, fuse or DC distribution equipment.

Before closing any breaker:

1. Keep the inverter and chargers switched off.
2. Keep the main DC disconnect open.
3. Keep all battery branches isolated.
4. Verify the polarity of every battery.
5. Verify the polarity of every series interconnection.
6. Verify positive and negative busbar identification.
7. Measure the polarity at the inverter DC input.
8. Check for unintended continuity between positive and chassis ground.
9. Check for unintended continuity between negative and chassis ground according to the approved grounding design.

Use correctly rated test instruments and insulated probes.

Stage 5: Measure Individual Battery and String Voltage

Record the open-circuit voltage of every battery before connecting parallel branches.

For a series string, measure:

• Each individual battery
• Each connection step
• Total string voltage
• Polarity of the complete string

For example, a string made from four compatible 12.8V batteries should produce approximately 51.2V nominal. The measured open-circuit voltage will depend on SOC and rest time.

For parallel strings, measure the total voltage of every string independently.

Do not close the parallel connection when string voltages are materially different. A voltage difference can create a high equalisation current between strings.

Manufacturer installation instructions commonly require individual batteries to be charged and balanced before series or series-parallel connection.

Stage 6: Verify Protection Devices

Inspect every fuse, breaker and disconnect.

Record:

• Device manufacturer and model
• Rated current
• DC voltage rating
• Interrupting capacity
• Fuse class
• Trip curve where applicable
• Cable size protected
• Installation location
• Polarity or direction requirements
• Open and closed position labels

For parallel batteries, verify that each branch has the required protection.

For series-parallel banks, verify that each complete series string has positive-side protection before joining the common busbar.

Check that the main protection device is suitable for the combined battery bank.

Stage 7: Configure the BMS Communication Network

Communication errors are a frequent cause of failed commissioning.

Before connecting the inverter communication cable, configure the battery network.

Depending on the product design, this may include:

• Selecting the master battery
• Assigning slave addresses
• Setting DIP switches
• Connecting battery-to-battery communication cables
• Installing a termination resistor
• Selecting CAN or RS485
• Selecting the inverter protocol
• Confirming firmware compatibility

Only one battery should normally use each communication address.

After configuration, check:

• Total number of batteries detected
• Total capacity reported
• Battery voltage reported
• SOC reported
• Maximum charge current
• Maximum discharge current
• Battery temperature
• Alarm status
• Communication status

Do not assume that an RJ45 connector uses standard Ethernet pin assignments. Use the communication cable specified for the battery and inverter combination.

Stage 8: Verify Inverter Battery Settings

Incorrect inverter settings can cause overvoltage alarms, low-voltage shutdowns or repeated BMS disconnection.

When closed-loop communication is available, confirm that the inverter correctly receives the battery limits.

When operating in voltage-control mode, configure values according to the battery supplier’s instructions.

Review:

• Battery chemistry
• Nominal voltage
• Bulk or absorption voltage
• Float voltage or float disable setting
• Low-voltage cut-off
• Restart voltage
• Maximum charging current
• Maximum discharge current
• Generator charging current
• Grid charging current
• Temperature compensation setting

Lead-acid charging profiles should not be copied directly to LiFePO4 batteries.

Stage 9: Perform Controlled Pre-Charge and Energisation

Before closing the main DC connection, confirm the approved pre-charge procedure.

A controlled energisation sequence may include:

1. Switch off AC input and output loads.
2. Open the main battery breaker.
3. Close one approved battery branch.
4. Activate the battery or master BMS.
5. Apply the pre-charge circuit.
6. Confirm that the inverter DC bus voltage rises correctly.
7. Close the main DC breaker.
8. Start the inverter.
9. Add remaining battery branches one at a time.
10. Check for alarms after each branch is connected.

The exact order depends on the battery and inverter architecture.

Stop immediately when there is:

• A large spark
• Unexpected breaker trip
• Reverse voltage indication
• Burning smell
• Rapid cable heating
• BMS short-circuit alarm
• Contactor chattering
• Abnormal inverter noise

Do not repeatedly reset protective devices without identifying the cause.

Stage 10: Initial Charging Test

Begin with a controlled charging current rather than the maximum available current.

During charging, record:

• Total battery current
• Individual branch current
• Battery voltage
• Highest cell voltage
• Lowest cell voltage
• Cell voltage difference
• Battery temperature
• BMS charge limit
• Inverter charge current
• Alarm history

For series strings, watch for one battery reaching its high-voltage protection limit earlier than the others.

For parallel batteries, check whether one unit is accepting substantially more current than the other units.

Allow the bank to reach the manufacturer’s recommended balancing region when required.

Stage 11: Controlled Discharge Test

Apply a known load and increase it gradually.

A practical sequence may include:

• Low load
• Medium load
• Normal operating load
• Short-duration peak load where approved

Record the same electrical and temperature data at each load level.

Confirm that:

• The inverter remains stable
• No battery disconnects unexpectedly
• Branch currents are reasonably distributed
• The main voltage drop is acceptable
• Cables and terminals remain within normal temperature
• The BMS reports the expected discharge limits
• SOC decreases consistently

The test load should not exceed the approved current rating of the batteries, BMS, protection devices or inverter.

Stage 12: Parallel Current-Sharing Test

Current sharing should be verified with a DC clamp meter.

For every parallel battery or string:

1. Apply a stable load.
2. Measure branch current.
3. Record the value.
4. Repeat during charging.
5. Compare branch temperatures.
6. Repeat at a higher approved current.

Equal current paths require consistent cable type, cross-sectional area, cable length, lugs and torque. Busbar-based connections are commonly used to improve balance.

A branch carrying persistently higher current should be investigated for:

• Shorter or larger cable
• Lower-resistance fuse
• Loose connection on another branch
• SOC difference
• Internal battery resistance difference
• BMS current limitation
• Firmware mismatch
• Battery capacity difference

Do not correct current imbalance by changing cable sizes randomly. Identify the cause and maintain a symmetrical design.

Stage 13: Voltage-Drop and Thermal Inspection

Electrical resistance generates heat under load.

Measure voltage drop across:

• Battery terminals
• Branch fuse
• Branch breaker
• Cable lugs
• Busbar connections
• Main breaker
• Main inverter cables

A thermal camera is useful for comparing identical connection points during charging and discharging.

A connection that is significantly warmer than similar connections may indicate:

• Loose hardware
• Poor crimping
• Incorrect lug size
• Oxidised contact surface
• Damaged fuse holder
• Undersized conductor
• Excessive branch current

Investigate abnormal temperature before releasing the system.

Stage 14: Alarm and Protection Testing

Where safe and supported by the equipment, verify:

• Battery communication-loss alarm
• High-temperature alarm input
• Low-SOC warning
• Emergency stop
• Main disconnect operation
• Inverter shutdown command
• Generator start signal
• Remote monitoring
• Alarm notification
• Battery branch isolation

Do not intentionally short-circuit batteries or force cells beyond their approved limits.

Use simulated signals or manufacturer-approved test methods.

Stage 15: Create a Commissioning Record

A professional commissioning report should include:

• Project name and location
• Installation date
• Installer
• Battery model and serial numbers
• Inverter model and serial number
• Battery configuration
• Cable sizes and lengths
• Fuse and breaker information
• Terminal torque values
• Firmware versions
• Communication protocol
• Inverter settings
• Individual battery voltages
• String voltages
• Charging test data
• Discharging test data
• Branch current measurements
• Temperature measurements
• Alarm test results
• Photographs of completed wiring
• Final acceptance signature

This baseline information is valuable when diagnosing future performance changes.

Quick Commissioning Checklist

Before handover, confirm:

• Batteries are mechanically secure
• All polarities are correct
• Series quantity is approved
• Parallel quantity is approved
• Battery and string voltages are matched
• Cables are correctly sized
• Cable paths are balanced
• Terminals are torqued correctly
• Branch fuses are installed
• Main DC protection is installed
• DC breakers have suitable voltage ratings
• BMS addresses are unique
• Master-slave communication is stable
• Inverter protocol is correct
• Pre-charge works correctly
• Charging test is complete
• Discharging test is complete
• Current sharing is acceptable
• No abnormal heating is present
• Monitoring and alarms are functional
• Commissioning data is recorded

Frequently Asked Questions

Can the inverter be connected before all batteries are switched on?

This depends on the system design. Some systems require the master battery to start first, while others require all branches to be available before inverter start-up. Follow the approved start-up sequence.

Why does one parallel battery show a different SOC?

Possible causes include different initial SOC, current-sharing imbalance, communication configuration, battery calibration differences or capacity variation.

Should every battery be fully charged before series connection?

Many manufacturers require batteries to be fully charged and balanced before series or series-parallel assembly. Follow the instructions for the specific battery model.

Can commissioning be completed without a clamp meter?

The system may operate, but branch current sharing cannot be properly verified without measuring individual currents. A DC clamp meter is strongly recommended for multi-battery installations.

When should terminal torque be rechecked?

Follow the manufacturer’s maintenance instructions. Reinspection after initial operation can help identify settling, cable movement or loose hardware, but batteries should be safely isolated before any torque inspection.

Conclusion

Commissioning is the final quality-control stage between installation and normal operation.

For series, parallel and series-parallel LiFePO4 battery systems, commissioning should verify:

• Configuration compatibility
• Voltage and polarity
• Mechanical integrity
• Protection coordination
• BMS communication
• Inverter settings
• Charging and discharging behaviour
• Parallel current sharing
• Voltage drop
• Connection temperature
• Alarm operation
• Complete project documentation

A battery bank that starts successfully is not automatically a correctly commissioned battery bank.

For HIZN Lithium energy storage projects, customers and system integrators can provide the inverter brand, inverter model, system voltage, power requirement, backup duration and proposed battery quantity before ordering. Pre-project technical confirmation helps reduce installation errors and speeds up on-site commissioning.