Overview
This architecture couples the buffer battery on the DC bus rather than on the AC side, so the battery and the charge points share the same power conversion stage. DC coupling removes one conversion step, improving round-trip efficiency and reducing response latency. It is the preferred topology for single-cabinet, all-in-one products where the battery, rectifier and charge controller are factory-integrated, and for high-power sites where 500-1200 A peak currents are required at 800-1000 V.
How it works
The grid feed is rectified once into a common DC bus. An energy management controller allocates DC power between the battery converter and the charge point converters with millisecond resolution. When a vehicle requests 400 kW but the grid can only supply 100 kW, the battery converter injects the difference; when the vehicle tapers, surplus flows back into the battery. Peak output currents of 600 A per cable and 2400 A across dual guns are achievable only with liquid-cooled cables and a DC bus that is sized for the full peak.
Advantages
- Higher round-trip efficiency than AC-coupled buffer systems
- Lower latency and tighter power-sharing between ports
- Compact single-cabinet or all-in-one form factor
- Fewer conversion stages means less hardware to maintain
- Natural fit for 800 V and 1000 V high-power platforms
- Factory-integrated and pre-tested before shipment
Considerations
- Battery and charger are vendor-coupled, limiting later sourcing flexibility
- DC bus fault protection and isolation are more demanding
- Higher peak design rating raises component cost
- Not all charger OEMs offer a DC-coupled battery option
- Field replacement of the battery may require OEM involvement
- Limited interoperability across brands compared with AC coupling
Applications
- All-in-one battery-integrated fast chargers
- Urban high-power charging without grid upgrade
- Truck and bus megawatt-class charging depots
- Retail fuel-station retrofits
- Marine and port charging
- Construction-site and temporary charging
Cost breakdown
For a battery-integrated DC charger the battery accounts for roughly 40-50% of hardware cost, the power modules and DC bus 25-35%, the cable and connector assembly 8-12%, and enclosure, cooling and controls the remainder. Liquid-cooled 600 A cable assemblies remain a disproportionate share of cost at the top end of the current range.
Market outlook
Battery-integrated DC charging is moving from niche to mainstream as grid connections become the binding constraint. Products such as the FreeWire Boost Charger 150 (160 kWh battery, 150 kW output) and the ADS-TEC ChargePost (up to 201 kWh, 300 kW output) established the category commercially, and Chinese vendors now offer comparable all-in-one cabinets at materially lower price points. The relevant market - EV DC charging stations - is forecast to grow from about USD 14.2 billion in 2025 to roughly USD 42.6 billion by 2030.