Megawatt Charging System (MCS) and ISO 15118: Charging the Heavy-Duty Fleet at 1 MW and Above

This article covers how MCS works, where it fits alongside CCS2, what ISO 15118 brings to the table, and what fleet and OEM integration teams need to plan for.

Why CCS2 was not enough

CCS2 (Combined Charging System, Type 2) is the European DC fast-charging standard for passenger cars and light commercial vehicles. It tops out at around 350 kW in production deployments, with theoretical limits near 500 kW. For a passenger car with a 70-100 kWh battery, this is more than adequate.

For a Class 8 truck with a 540 kWh battery, charging at 350 kW takes more than 90 minutes from low SoC to high SoC, well above the 45-minute mandatory rest period drivers actually have available. The bottleneck is not just the time but the connector: at 500 A continuous current, the CCS2 cable becomes thick, heavy, hard to handle, and thermally limited.

MCS solves this by stepping current up to 3,000 A and voltage to 1,250 V, with active liquid cooling in both the charger and the cable. A 1.0 MW charge into a depleted 540 kWh battery takes about 30 minutes; a 1.5 MW charge into the same pack takes around 22 minutes. That fits inside the rest period.

MCS specifications at a glance

ISO 15118-20: what changed from 15118-2

ISO 15118 is the international standard for vehicle-to-grid communication during charging. The first widely-deployed edition, ISO 15118-2 (2014), defined Plug and Charge over CCS2 and basic AC charging communication. The second edition, ISO 15118-20 (2022), is the version MCS targets. The difference is structural, not incremental.

• Bidirectional power transfer (V2G). 15118-20 supports vehicle-to-grid, vehicle-to-home and vehicle-to-load natively, with the metering and certificate-management primitives the V1G version lacked.
• Smart charging at scale. 15118-20 supports dynamic charging schedule negotiation, allowing depot-level power management to flatten peak loads across multiple charging vehicles.
• Plug and Charge with multiple contracts. 15118-2 PnC was tied to a single contract per vehicle. 15118-20 supports multiple contracts, which is essential for fleet scenarios where the same truck charges at the home depot, at a motorway stop, and at a customer site under three different billing arrangements.
• TLS 1.3 and stronger PKI. 15118-20 mandates modern cryptography. The certificate hierarchy is more complex and fleet-scale certificate provisioning becomes a CSMS topic (see ECE R155 and ISO 21434).
• Wireless and pantograph charging support. 15118-20 anticipates non-conductive charging interfaces, relevant for buses and certain port applications.

The depot picture: where MCS, CCS2 and overhead chargers all coexist

For most heavy-duty fleet operators, the answer is not MCS-only or CCS2-only. A typical 2027-2030 depot will host all three approaches:

1. Overnight CCS2 at the home depot for the bulk of the fleet, charging slowly at 50-150 kW over 8-10 hours of dwell time.
2. MCS at high-throughput hubs (regional distribution centers, motorway stops, port terminals) for opportunity charging during driver rest periods.
3. Pantograph or overhead conductive charging for fixed-route urban buses and certain port applications, where the vehicle returns to a fixed point repeatedly.

The integration challenge is on the vehicle side. A truck designed for MCS-only cannot use the existing CCS2 infrastructure; a truck with CCS2 only cannot use the new MCS hubs. Most OEMs are converging on dual-port designs: MCS as primary, CCS2 as fallback. This adds packaging cost and a second connector, but it removes the operational risk of stranding a truck at a charge point that does not match.

Vehicle-side integration: what changes for the OEM

Adding MCS to a heavy-duty platform is not a simple cable swap. The architecture changes touch four subsystems.

Battery system

A 1.5 MW charge at 1,000 V means 1,500 A flowing into the pack. Cell-level current sharing, busbar sizing and contactor ratings have to be designed for this peak. Most existing heavy-duty packs were sized for ~500 A peak; MCS-capable packs need 1,500-3,000 A peak rating, which often forces a different cell format or topology.

Thermal management

1 MW into a battery means 1-3% energy loss as heat at high charge rates, depending on chemistry and SoC. That is 10-30 kW of heat to dissipate during the charge, on top of any solar and ambient gain. Most existing heavy-duty thermal systems are sized for traction load, not for fast-charge load. MCS-capable platforms typically require uprated chillers, larger cold-plate systems, or in some cases immersion cooling.

HV protection

1,250 V exceeds many existing HV component voltage ratings. Contactors, fuses, isolation monitoring, and BMS sensing all have to be re-rated. ECE R100 isolation requirements scale with voltage, so the isolation strategy on an MCS platform is meaningfully different from a 600 V platform.

Charge control

Implementing ISO 15118-20 properly requires a charge controller that supports TLS 1.3, certificate management at fleet scale, V2G negotiation, and dynamic schedule updates. This is a different software complexity from the 15118-2 implementations that exist today.

The infrastructure picture: when MCS becomes available

The MCS rollout is happening in three waves:

• 2024-2025: pilot deployments. First MCS chargers at OEM and fleet test facilities, plus initial demonstration sites in Germany, the Netherlands and California.
• 2026-2027: motorway corridor rollout. Major European logistics corridors and US Interstate routes hosting first-generation 1.0-1.5 MW MCS chargers, often co-located with CCS2.
• 2028-2030: high-power deployment. Second-generation MCS chargers approaching 3 MW, denser network coverage, integration with grid-scale storage to manage peak demand.

For OEMs releasing trucks in 2027 and beyond, MCS support is becoming a baseline expectation. For fleet operators planning depot infrastructure now, the design choice is whether to install MCS-ready conduits and transformer capacity even before the chargers themselves arrive, since the civil-works component of an MCS station is the long-lead item.

Where integration partners add value

Integration of MCS into a heavy-duty program is not a bolt-on. It is a system-level change that touches battery, thermal, HV protection, charge control, EMC (charging-mode emissions at 1 MW are a different problem than at 350 kW), and homologation. The high-leverage moments where a co-developer pays back the investment are:

1. Architecture review with MCS in scope from concept, sizing the battery, thermal, and HV systems for 1 MW peak rather than retrofitting.
2. EMC pre-compliance during charging mode at full MCS power, well before homologation slot.
3. ISO 15118-20 stack integration with the OEM’s existing telematics and certificate management.
4. Depot interoperability testing with both MCS and CCS2 hardware, on real fleet routes.