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LG RESU FLEX: High-voltage battery with Tetris system

Photovoltaic knowledge
Updated on 21. June 2022
6 min. Reading time
Marcel Melle
Marcel Melle

With LG RESU FLEX, LG Energy Solution is introducing a home system for 3-phase hybrid inverters to the market for the first time. The Tetris principle offers you a lot of installation options. We show you how flexible the new high-voltage battery system is.

LG Energy Solution presents the LG RESU FLEX high-voltage battery system for domestic use. It comes in 3 different sizes with a usable storage capacity ranging from 8.6 to 17.2 kWh. It is expandable by 2 to 4 battery modules on a modular basis. The new LG battery system is compatible with many hybrid inverters. LG has also decided against stackable module units to make the system suitable for both floor and wall mounting. With 36 different wall mounting constellations, LG has increased flexibility.

The new LG high-voltage battery explained in numbers

The LG RESU FLEX has 2 main components: a control unit, the Battery Protection Unit (BPU), and at least 2 battery modules, the Battery Module Assemblies (BMA), with 4.3 kWh. The system can be expanded to up to 4 battery modules. Thus, it achieves a usable storage capacity of 17.2 kWh. If a larger storage capacity is required, 2 systems can also be connected in parallel. Combined, the high-voltage battery systems can offer a storage capacity of up to 34.4 kWh.

A BMA has a voltage of 132 V. If connected in series, 4 battery modules reach a voltage of 508 V. The LG RESU FLEX variants compared:

LG RESU FLEX8.612.917.2
Usable Storage Capacity8.6 kWh12.9 kWh17.2 kWh
Max. Charge / Discharge Power4.3 kW6.5 kW8.5 kW
Voltage Range192−265 V288−398 V384−531 V
Cell TechnologyNMC
Structure2 BMA, 1 BPU3 BMA, 1 BPU4 BMA, 1 BPU
Weight BPU / BMA16.5 kg / 48.9 kg
System Expansion CapacityMax. 2 systems in parallel
Installation DesignFor wall and floor mounting
Planned CompatibilitiesSMA, Fronius, Kostal, GoodWe

You can find more information about the product here.

Compatibilities of the LG RESU FLEX

LG Energy Solution will offer compatibility with 4 manufacturers of 3-phase hybrid inverters. The LG RESU FLEX can be integrated into one single system with the GoodWe ET plus, the Kostal Plenticore plus, the Fronius Symo Gen24 plus, and the SMA hybrid inverter. The 1-phase high-voltage hybrid inverter Primo Gen24 plus as well as the SMA Sunny Boy Storage 3.7-6 will also be compatible with the LG RESU FLEX after completion of the field tests and approval process.

Flat, flatter, LG RESU FLEX

The battery modules and the control unit have a depth of 14.8 cm. LG installs smaller JS1 battery cells and saves the DC/DC converter. In this way, the manufacturer creates a remarkably thin battery system.

Positioning the LG RESU FLEX correctly

You usually mount the high-voltage battery next to the hybrid or battery inverter in the basement or utility room. If the outside temperature is between at least -10 °C and a maximum of 50 °C, you can also install the battery system outside. At temperatures below -10 °C, the LG RESU FLEX switches off automatically. However, you should avoid direct sunlight. The optimal ambient temperature is between 20 °C and 30 °C.

Mounting on the floor

You can mount the LG RESU FLEX either on the floor or on the wall. For floor mounting, you connect the battery modules behind the control unit. First, you attach a basic standing bracket to the control unit and to each battery module. Screw a bracket to the backmost battery unit and mount it on the wall with a small gap. Ensure that there is a safety distance of 30 cm next to and 50 cm above the LG RESU FLEX. Add the remaining battery modules one by one. Connect them to each other using the connecting cables from the terminal block in the middle. Pass the cables through the cable ducts provided along the sides of the module. At the end, put the control unit on.

With the optional floor mounting kit, the high-voltage battery system stands 13.8 cm above the ground and can withstand minor flooding. You need an extra mounting kit for each battery module and for the control unit. The kit also includes wheels so that the battery can be moved.

Mounting on the wall:

For wall mounting, you have 36 different geometric arrangement options. You can simply adapt the configuration according to the conditions on site. Refer to LG's quick installation manual to find out which configurations are possible. You need the corresponding wall-mounting kit for the installation. For this type of installation, one kit per battery module as well as one kit for the control unit is necessary.

First, screw the mounting devices to the wall. The battery units and thus also the mounting kits must be flush with each other at the sides and without offset. Please consider the safety distance: 50 cm above, 30 cm to the left and right and 15 cm below the mounting bracket must be left free. Before you insert the BMA and the BPU into the bracket, screw another bracket element to the back of each module. Now place all the module elements in the brackets. Then connect the battery modules to each other using the connecting cables from the terminal block in the middle and then the last one to the control unit. For wall mounting, you also route the cables through the cable ducts provided along the sides of the module.

In addition to the wall bracket, the wall mounting kit also includes a design cover that you place on the front of the battery modules. Since the control unit does not have a design cover, you have one in reserve.

In both the installation methods, you then connect the control unit to the inverter using a 6 mm2 battery cable, a communication cable (CAN or RS485) and the Ethernet cable. Afterwards, you activate the LG RESU FLEX via the RESU-Monitor app for Android and iOS. Once connected, the app shows you the actual current flow status and the storage status of the LG RESU FLEX high-voltage battery system.

Installation requirements

In order to install the LG RESU FLEX, you must first take LG's free certification training. The training takes place online, allowing you to participate from anywhere. You do not have to register beforehand. At the end of the training, you need to take an online test. If you pass, you can download your certificate from the LG website and become a certified installer for the LG RESU FLEX high-voltage battery. Moreover, the certificate gives the product a full product warranty.


The new LG RESU FLEX high-voltage battery system is a new addition to the RESU Prime high-voltage battery. For the first time, LG offers you a home system for 3-phase hybrid inverters. Multiple mounting options make the system extremely flexible. LG is also working intensively to increase the number of compatibilities so that the new battery system also works with Fronius. Combination with SolarEdge is not possible.

In summary

  • The LG RESU FLEX comes in 3 storage capacities and is the manufacturer's first home system for 3-phase hybrid inverters.
  • Two mounting options as well as the Tetris principle for wall mounting offers more flexibility.
  • The high-voltage battery is compatible with many manufacturers, including Fronius.
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