Marstek Venus E Gen 3.0 5.12kWh plug-in AC battery5.12kWh AC-coupled LFP storage with 2.5kW bidirectional inverter and backup socket

Overview

Venus E Gen 3.0 (MST-BIE5-2500) adds 5.12kWh of LFP storage to an existing PV system through one AC cable with a Euro 16A plug. It charges at 2.5kVA, discharges at 800VA by default or 2.5kVA where permitted, and supplies 2.5kVA from its backup socket, with 3.5kVA for 10s. Compared with Gen 2.0, Marstek has reduced the volume by 38.5%, moved to a die-cast aluminium housing and added RJ45 ports for Ethernet and RS-485. At 90% depth of discharge, about 4.6kWh is available per cycle.

• 5.12kWh LFP, 51.2V 100Ah, 90% depth of discharge
• 2.5kW charging; 800W default or 2.5kW output
• 2.5kVA backup socket, 3.5kVA peak for 10s
• Wi-Fi, Bluetooth, Ethernet and RS-485 with open API
• IP65, natural convection, -20…+55°C
• CEI 0-21, VDE 4105 and EN 50549-1 listed

How it works

Venus E Gen 3.0 connects on the AC side only: one cable links the GRID port to a household socket, and the unit charges from surplus PV or the grid and discharges back into the home circuit. It works alongside any existing inverter or microinverter because it never touches the DC side. A separate BACKUP socket supplies loads plugged into it during an outage. The two ports must never both be connected to the mains, as the manual warns of tripping or damage.

Inside, a 51.2V, 100Ah prismatic LFP pack feeds an isolated inverter built on an integrated PCB, which Marstek says halves internal wiring, all in a die-cast aluminium housing. Marstek specifies more than 6,000 cycles at 25°C and a battery-to-AC efficiency above 93.5%.

Installation and compatibility

The unit must stand upright, never tilted or lying down, and the supplied brackets can fix it to the wall. Brick or concrete is preferred; drywall or timber is allowed only if flame-retardant and strong enough for the 60kg weight. Keep the clearances drawn in the manual free for cooling and fit each branch circuit with its own breaker. Grid-tied operation needs approval from the local network operator.

Output is limited to 800W by default; the 2.5kW setting may only be used where the utility or authority permits it. The brochure lists NF-EN 50549-1, VDE 4105/VDE 0124, G98, CEI 0-21, PN-EN 50549-1/-2, TOR R25, UNE 217001/217002 and NTS 631, plus IEC 62040 and IEC 62477.

Operating modes and meters

Self-consumption mode needs a meter: Marstek CT002 or CT003, Shelly Pro 3EM, Shelly EM Gen3, Shelly Pro EM-50, everHome EcoTracker IR or the HomeWizard P1 meter. Third-party meters handle one unit per phase, and for several units Marstek advises three-phase total compensation. AI mode uses Nord Pool, Tibber or Octopus prices; manual mode follows a schedule; UPS mode keeps the battery full for outages.

Several units can operate in parallel on the grid side, and with the Marstek SmartBox up to three units give single-phase whole-home backup of 7.5kW and 15.36kWh. In Marstek's system diagram for this setup, the existing on-grid PV system keeps generating during an outage while the SmartBox supplies the backup line of the home.

Monitoring and settings

Setup runs in the Marstek app via Bluetooth, followed by Wi-Fi; a LAN port gives a wired link where the signal is weak. The app sets the 800W or 2,500W grid limit, a depth-of-discharge window from 30% to 88%, energy prices and backup operation, and it handles firmware updates. A local API and Modbus over RS-485 allow integration with Home Assistant, ioBroker or an external EMS.

Questions and answers