Direct Answer

A containerized battery energy storage system can store several megawatt-hours of electricity in one transportable enclosure. TLS currently lists configurable BESS platforms with an energy capacity range of 3.73 to 6.26 MWh. The actual capacity of a project, however, depends on the selected battery system, container layout, cooling method, operating limits and required service life.

The MWh figure describes how much energy the system can hold. It does not, by itself, show how quickly that energy can be delivered, how long the system will run at a given load or how much energy will remain usable over time.

What Does MWh Mean in a BESS Container?

Megawatt-hours measure energy. One megawatt-hour is the amount of energy delivered by one megawatt of power for one hour.

For example, a 5 MWh battery could theoretically deliver 5 MW for one hour or 2.5 MW for two hours. In practice, the usable result also depends on operating limits, conversion losses, auxiliary consumption and the control strategy.

Power and energy therefore answer different questions:

• MW tells you how fast the system can charge or discharge.
• MWh tells you how much energy the system can store.
• Duration links the two. A 5 MWh system delivering 2.5 MW has a nominal two-hour duration.

Why Does Capacity Vary Between BESS Containers?

The external container size is only one factor. The usable capacity is determined by the complete internal arrangement.

Battery selection

Different cells, modules and racks have different dimensions, energy density and operating limits. The selected battery platform determines how much energy can be installed within the available space.

Equipment layout

A BESS container also needs room for thermal management, electrical protection, cable routes, fire-safety equipment and maintenance access. Increasing the number of battery racks without preserving these functions does not create a practical design.

Cooling method

TLS offers both liquid-cooled and air-cooled configurations. Each method uses space differently and must be matched to the battery heat load, local climate and operating profile. Cooling selection is therefore part of capacity planning, not a separate decision made after the racks are placed.

Transport and structural limits

Battery systems are heavy. The final layout must account for total mass, load distribution, lifting, transport restrictions and the foundation at the destination. A physically possible rack arrangement may still be unsuitable if it creates unacceptable transport or structural conditions.

Operating reserve and service life

A battery is not normally operated across its entire theoretical range on every cycle. Control limits may reserve part of the capacity to protect the cells, meet warranty conditions or maintain long-term performance. Project teams should compare usable energy under agreed conditions, not only the maximum nameplate figure.

Does a Higher MWh Rating Always Mean a Better BESS?

No. The right capacity is the one that matches the project duty.

A solar project may need to move daytime generation into the evening, while a commercial facility may use storage to reduce short demand peaks. Adding more MWh can increase cost, weight and footprint without improving the intended service. Capacity should follow the operating requirement.

How Do TLS Integration Levels Affect the Capacity Decision?

TLS presents three BESS delivery levels: container enclosure, semi-integrated and fully integrated. These terms describe the supply scope, not a fixed energy rating.

• A container enclosure provides a configurable foundation for a customer or system integrator to install its chosen battery and related equipment.
• A semi-integrated container includes battery racks and selected auxiliary systems while retaining flexibility for project-selected components.
• A fully integrated solution coordinates the agreed battery system, thermal management, protection and electrical integration as a complete package.

The same general capacity target may be approached through different delivery scopes. The final quotation and technical documents should state what equipment is included and which performance values apply.

What Else Should Be Checked Besides MWh?

A useful BESS comparison should include:

• rated power and expected discharge duration;
• usable energy at the agreed operating conditions;
• battery type, cycle requirements and expected capacity retention;
• air- or liquid-cooling arrangement;
• ambient temperature, altitude and corrosion conditions;
• enclosure protection and site installation requirements;
• fire-safety and grid-connection interfaces; and
• transport, lifting and foundation constraints.

TLS lists IP55 protection, C5 corrosion protection and an operating range of −30°C to +55°C among its current BESS platform specifications. These are configurable platform capabilities; the applicable values must be confirmed for the specific system and project.

 FAQ

Is 6.26 MWh the capacity of every TLS BESS container?

 No. TLS lists 3.73–6.26 MWh as its current platform range. The final capacity depends on the selected configuration and agreed project conditions.

Does the container capacity include the PCS? 

Energy capacity refers to the battery storage. The PCS may be installed inside the container or supplied separately, depending on the project scope.

Should buyers compare nominal or usable energy?

Usable energy is usually the more meaningful project value because it reflects the energy available within the agreed operating window. The basis of measurement should be stated clearly.

Conclusion

A BESS container does not have one universal capacity. TLS currently offers platforms in the 3.73–6.26 MWh range, but the correct selection depends on power, duration, battery choice, cooling, site conditions and lifecycle requirements. The most useful comparison is not simply “Which container has the highest MWh?” but “Which configuration delivers the required usable energy for this application?”

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Direct Answer

The difference between container enclosure, semi-integrated and fully integrated BESS containers is the supply boundary:

• BESS enclosure typically provides the structural container and battery racks, leaving most battery, cooling, fire, control and electrical integration to the customer or system integrator.
• A semi-integrated BESS container adds defined auxiliary systems—commonly cooling, fire protection, lighting and earthing—while preserving customer choice for batteries, PCS, EMS or other equipment.
• A fully integrated BESS container includes the agreed battery system, BMS, DC collection, thermal management, safety systems and auxiliary electrical systems as one factory-integrated package.

 How Do the Three Delivery Models Compare?

Important: “Fully integrated” does not automatically mean that the PCS, transformer, medium-voltage switchgear, site EMS, civil works or grid interconnection are included. The contract must state the AC and DC boundaries.

 When Is a Basic BESS Enclosure the Better Choice?

A basic enclosure suits buyers or integrators that already control the battery technology and balance-of-system design. It offers the most integration freedom but leaves more interface responsibility with the buyer.

Choose this model when:

• battery packs and auxiliary systems are already nominated;
• the integrator owns the system safety case and certification route;
• local content or customer-approved vendors must be used;
• the project team can manage structural, thermal, electrical and fire interfaces;
• more installation and testing outside the enclosure supplier's scope is acceptable.

Compare total installed cost, not enclosure price alone: later integration can require redesign, rework or duplicate testing.

 When Does Semi-Integrated Supply Make Sense?

Semi-integrated supply suits buyers that want the enclosure manufacturer to coordinate racks and key auxiliaries while retaining their preferred battery, PCS or controls. Battery heat loads, coolant conditions, gas-release assumptions, detector logic and emergency actions must be defined early so the auxiliaries match the selected battery system.

 When Is a Fully Integrated Container Appropriate?

A fully integrated container is appropriate when one party must deliver and test the agreed DC battery package as a coordinated unit. It reduces internal handoffs but does not remove project-level integration.

The project still needs to define:

• duty cycle, usable energy and power;
• AC/DC point of connection and PCS/transformer arrangement;
• EMS, SCADA, grid protection and communication interfaces;
• fire-code and authority requirements;
• foundations, spacing, transport and commissioning responsibility.

“Plug-and-play” should be read as reduced field integration within a stated boundary, not as zero onsite engineering or testing.

 Who Owns System Certification and Safety Evidence?

The responsibility matrix must identify who owns complete-system certification and supporting evidence. Component certificates alone do not demonstrate conformity of the assembled BESS.

For projects using North American requirements, UL Solutions describes UL 9540 as a safety standard for complete energy storage systems and equipment. UL 9540A is a test method used to evaluate thermal-runaway fire propagation behavior; it is not a product certification label for the container by itself.

For grid-connected electrochemical systems, IEC 62933-5-2:2025 addresses safety across the BESS lifecycle and the interaction of subsystems. The applicable codes, editions, test levels and approving authorities must be selected for the installation jurisdiction.

 What Must the Responsibility Matrix Include?

Assign design, supply, connection, testing, approval and warranty responsibility for:

• cells, modules, racks, BMS and internal DC system;
• PCS, transformer and switchgear;
• cooling, fire protection and auxiliary power;
• enclosure structure and environmental protection;
• EMS, SCADA and communications;
• FAT, transport, installation, SAT, commissioning and warranty.

Each interface also needs agreed values for voltage, current, heat load, coolant conditions, communication protocol, connection point and fail-safe state.

What Should Be Verified at FAT and SAT?

FAT should verify the completed container scope: installation, electrical safety, BMS communications, cooling controls, alarm logic, emergency shutdown and simulated sequences. SAT should verify site grounding, PCS and transformer integration, EMS/SCADA, field connections, fire interfaces and charge/discharge performance.

FAQ

1.  Is a semi-integrated BESS container supplied with batteries?

Not necessarily. TLS describes its semi-integrated option as including racks and key auxiliary systems while allowing customers to select preferred battery, PCS or EMS technologies. The project quotation controls the final scope.

2.  Does fully integrated mean grid-ready?

Only if the grid-side equipment, controls, approvals and site works are included and completed. A fully integrated DC container may still require external PCS, transformer, switchgear and plant controls.

3.  Can certified components create a certified BESS automatically?

No. Certification of individual components does not automatically certify their assembled system or installation. The project must define the system-level conformity and approval route.

4.  Which option has the least interface risk?

The option with the clearest single-point responsibility across the relevant systems usually has fewer handoffs. A fully integrated container can reduce interfaces, but unresolved site and AC-side boundaries can still create risk.

 Conclusion

Select a BESS delivery model by deciding who will own integration—not by choosing the most complete-sounding label. A basic enclosure maximizes buyer control, a semi-integrated container transfers selected auxiliary systems to the enclosure supplier, and a fully integrated container consolidates the agreed battery package. The decisive document is a responsibility matrix that defines every component, interface, test, approval and warranty boundary.

Send the application, equipment layout, power profile, operating environment, certification needs, quantity and delivery location to sales@tls-containers.com. TLS supports engineering, integration, manufacturing, testing and worldwide delivery.

No. An IP55 rating means a BESS enclosure provides defined protection against dust and water jets under specified test conditions. It does not mean the container is watertight, floodproof, submersible or protected against every form of moisture.

For a battery energy storage system, IP55 is an important enclosure requirement because batteries, control equipment and electrical connections are commonly installed outdoors. However, the rating must be interpreted correctly and supported by drainage, condensation control, corrosion protection and maintenance.

What Does IP55 Mean?

The IP Code is defined by IEC 60529. In “IP55,” the two digits describe different types of ingress protection:

• The first 5 addresses solid-particle protection. The enclosure is dust-protected, meaning dust entry is limited to a level that does not interfere with satisfactory operation. It is not classified as completely dust-tight.
• The second 5 addresses water protection. The enclosure is protected against water jets directed from different directions under the standard test conditions.

The rating describes the tested enclosure configuration. It does not create a general guarantee for every outdoor condition.

What Does IP55 Protect a BESS Container Against?

An IP55 enclosure is intended to reduce harmful ingress from common outdoor exposure such as:

• airborne dust;
• wind-driven particles;
• rain reaching the enclosure from different directions;
• water jets within the applicable test conditions; and
• routine outdoor operation when doors, panels and penetrations are properly closed.

This protection helps separate sensitive internal equipment from the external environment. It is especially relevant at doors, service panels, cable entries, ventilation openings and joints between structural sections.

IP55 applies only when the complete enclosure remains in its rated operating condition. An open door, removed service panel, damaged gasket or unsealed cable entry changes that condition.

What Does IP55 Not Prove?

IP55 does not prove that a BESS container can withstand:

• flooding or standing water above the enclosure base;
• partial or complete immersion;
• continuous high-pressure cleaning;
• water entering through doors left open during maintenance;
• condensation forming inside the enclosure;
• long-term coating resistance in a corrosive atmosphere;
• drainage failure or blocked outlets;
• ice, snow accumulation or freeze-thaw damage; or
• water exposure beyond the tested configuration and conditions.

This distinction matters because water can reach electrical equipment without penetrating directly through an exterior wall. Moist air may enter during door opening, condense on cold surfaces and create internal droplets even when the external enclosure meets IP55.

Why Is “Waterproof” the Wrong Description?

“Waterproof” has no single engineering meaning. It may be interpreted as rain-resistant, jet-resistant, flood-resistant or submersible. These are different conditions and require different evidence.

Calling an IP55 BESS container waterproof can therefore create a false expectation. A more accurate statement is:

Which Parts Determine the Enclosure Rating?

The rating depends on the complete enclosure boundary, not only the steel shell. Common weak points include:

• Doors and Gaskets
• Cable and Pipe Penetrations
• Ventilation Openings
• Roof and Panel Joints
• Base and Drainage
•  

Is IP55 the Same as Corrosion Protection?

No. IP rating and corrosion protection address different risks.

• IP55 addresses ingress of solid particles and water under defined test conditions.
• A corrosion-protection system addresses degradation of materials caused by humidity, salt, chemicals and atmospheric exposure.

A container can pass an IP55 water test and still corrode prematurely if its coating system, surface preparation or material selection is unsuitable for the site. It can also have a strong corrosion-protection system but fail to control water entry at a damaged seal. For coastal or industrial projects, IP rating and corrosion category should be specified separately.

Is IP55 Enough for Every BESS Site?

Not automatically. The required enclosure protection should come from the actual site risk assessment.

The project should consider:

• rainfall intensity and wind exposure;
• dust and sand conditions;
• risk of flooding or poor site drainage;
• coastal salt and industrial pollutants;
• snow, ice and freeze-thaw cycles;
• cleaning methods used by maintenance teams;
• door-opening frequency;
• external cable and coolant connections; and
• applicable electrical and installation requirements.

How Can IP55 Performance Be Maintained?

Ingress protection is not permanent without inspection. Maintenance should include:

• checking door seals for cracking, compression loss and contamination;
• confirming that hinges and latches maintain even gasket pressure;
• inspecting cable glands and pipe seals;
• cleaning louvers and filters without damaging weather barriers;
• keeping roof and base drainage paths clear;
• repairing coating damage before corrosion reaches sealing surfaces;
• checking for internal condensation or water staining; and
• reviewing any new field penetration before modification.

After structural repair, door replacement or major cable work, the affected boundary should be inspected and retested when required by the project quality plan.

How TLS Applies IP55 to BESS Containers

TLS Energy lists IP55 as a core protection level for its configurable BESS platform. TLS has also published its use of water-spray testing to verify enclosure sealing before delivery.

The final design still depends on the project configuration. Cooling equipment, doors, cable entries, fire-safety interfaces and site connections must be coordinated so that the intended enclosure protection is maintained after installation.

FAQ

1. Can an IP55 container be pressure-washed?

Not simply because it is IP55. Cleaning pressure, nozzle distance, direction and duration may exceed the rated or tested water exposure. The manufacturer’s cleaning instructions should be followed.

2. Is IP55 dust-tight?

No. The first digit 5 means dust ingress is limited so it does not interfere with satisfactory operation. A completely dust-tight enclosure uses a higher solid-particle protection classification.

3. Does IP55 prevent condensation?

No. Condensation is controlled through thermal design, humidity management, insulation, heating or dehumidification, airflow and operating procedures.

4. Does every component inside an IP55 container have to be IP55?

Not necessarily. The enclosure may provide the environmental boundary for internal components. Equipment outside that boundary or exposed when doors are open must be assessed separately.

Conclusion

IP55 does not make a BESS container waterproof. It establishes defined protection against dust and water jets for a tested enclosure configuration. Reliable outdoor performance also requires properly designed penetrations, drainage, condensation control, corrosion protection, suitable foundations and ongoing seal maintenance.

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