A Fronius Reserva battery is not installed on its own: it forms part of a system in which the inverter, the energy meter and —if you want a backup system— the switching components must be carefully selected and properly interconnected.
This guide sets out the requirements and steps as set out in the official Fronius documentation. This is not a substitute for the equipment manual or a qualified installer: The installation must be carried out by authorised personnel, and the necessary arrangements must be made with the supplier.
| Element | What’s it worth? | Note |
|---|---|---|
| Hybrid inverter | Fronius Primo GEN24 Plus, Symo GEN24 Plus or Verto Plus, including SC versions | The suffix Plus indicates battery input. A GEN24 without ‘Plus’ does not support storage |
| Energy meter | Smart Meter 63A-1, 63A-3, 50kA-3 · Smart Meter TS 100A-1, TS 65A-3, TS 5kA-3 · Smart Meter IP | Essential: measures consumption and mains power |
| Battery | Reserve 6.3 / 9.5 / 12.6 / 15.8 | Compatibility depends on the inverter |
Two points about meters that are often overlooked:
Choosing the wrong transformer is a common mistake, and it is not detected until the system is commissioned.
Primo GEN24 Plus inverters (single-phase) only support Reserve 6.3 and 9.5. They are not compatible with either the 12.6 or the 15.8, regardless of their power rating. If you need more than 9.45 kWh, you will need a three-phase inverter.
And the charging and discharging power is not determined by the battery alone: it is determined by the combination. This is the official table of nominal DC power:
| Investor | Reserve 6.3 | Rating: 9.5 | 12.6 | 15.8 |
|---|---|---|---|---|
| Primo GEN24 3.0 Plus | 3.0 kW | 3.0 kW | — | — |
| Primo GEN24 3.6 Plus | 3,6 kW | 3,6 kW | — | — |
| Primo GEN24 4.0 Plus | 4.0 kW | 4.0 kW | — | — |
| Primo GEN24 4.6 Plus | 4,5 kW | 4.6 kW | — | — |
| Primo GEN24 5.0 Plus | 4,5 kW | 5.0 kW | — | — |
| Primo GEN24 6.0 Plus | 4,5 kW | 6.0 kW | — | — |
| Primo GEN24 8.0 Plus | 4,5 kW | 6.75 kW | — | — |
| Primo GEN24 10.0 Plus | 4,5 kW | 6.75 kW | — | — |
| Investor | 6.3 | 9.5 | 12.6 | 15.8 |
|---|---|---|---|---|
| Symo GEN24 3.0 Plus | 2.56 kW | 3.0 kW | 3.0 kW | 3.0 kW |
| Symo GEN24 4.0 Plus | 2.56 kW | 3.84 kW | 4.0 kW | 4.0 kW |
| Symo GEN24 5.0 Plus | 2.56 kW | 3.84 kW | 5.0 kW | 5.0 kW |
| Symo GEN24 6.0 Plus | 4,5 kW | 6.0 kW | 6.0 kW | 6.0 kW |
| Symo GEN24 8.0 Plus | 4,5 kW | 6.75 kW | 8.0 kW | 8.0 kW |
| Symo GEN24 10.0 Plus | 4,5 kW | 6.75 kW | 9.01 kW | 10.0 kW |
| Symo GEN24 12.0 Plus SC | 4,5 kW | 6.75 kW | 9.01 kW | 11.26 kW |
| Investor | 6.3 | 9.5 | 12.6 | 15.8 |
|---|---|---|---|---|
| Verto Plus 15.0 | 2.56 kW | 3.0 kW | 3.0 kW | 3.0 kW |
| Verto Plus 17.5 | 2.56 kW | 3.84 kW | 4.0 kW | 4.0 kW |
| Verto Plus 20.0 | 2.56 kW | 3.84 kW | 5.0 kW | 5.0 kW |
| Verto Plus 25.0 | 4,5 kW | 6.0 kW | 6.0 kW | 6.0 kW |
| Verto Plus 30.0 | 4,5 kW | 6.75 kW | 8.0 kW | 8.0 kW |
| Verto Plus 33.3 | 4,5 kW | 6.75 kW | 9.01 kW | 10.0 kW |
How to read these tables. A surprising fact: with a Symo GEN24 10.0 Plus, a Reserva 6.3 only delivers 4.5 kW, whilst a 15.8 delivers 10 kW. Fitting a small battery to a large inverter limits the backup power, not just the runtime. If the aim is to power high-demand loads whilst cutting, capacity matters just as much as kWh.
These figures refer to direct current power. The alternating current power reaching the loads is slightly lower, as the inverter’s efficiency must be taken into account.
In this case, the manual is much more restrictive than is generally assumed.
This list is surprising, and constitutes grounds for the warranty to be voided:
If your project involves crop or livestock farming — which is common in self-consumption — the location must be carefully considered.
| Model | Height × width × depth | Weight |
|---|---|---|
| Reserve 6.3 | 890 × 772 × 176 mm | 86.5 kg |
| Rating: 9.5 | 1,140 × 772 × 176 mm | 120 kg |
| Reserve 12.6 | 1,390 × 772 × 176 mm | 153.5 kg |
| Reserve 15.8 | 1,640 × 772 × 176 mm | 187 kg |
At 176 mm deep, the tower fits into narrow corridors and rooms. But 187 kg In the large configuration, a firm floor is required: each module weighs 33.5 kg and is stacked on top of the base.
Regarding earthing: The modules are already connected to one another via a common earth connection, which ensures equipotentiality. An additional earth connection is neither required nor permitted on individual modules. The protective conductor is secured using the M4x10 TX20 screw supplied, to 3 Nm of torque.
The backup system does not simply connect to the mains; it needs to communicate with the inverter.
| Connection | Specification |
|---|---|
| Data communication | RJ45, minimum CAT 5 STP shielded. Maximum 30 m |
| Inverter ↔ battery cable | Maximum 40 m |
| DC cables | They must comply EN 50618 or IEC 62930 |
| DC terminals (PRO Reserve) | Stäubli MC4 EVO STO, 6 or 10 mm², stripped to 7 mm |
| Protective conductor | Tinned copper 2.5–6 mm², 4 mm drill bit, 3 Nm |
Cables that do not comply with EN 50618 or IEC 62930 have a lower current-carrying capacity, and it is the installer’s responsibility to ensure they are correctly sized.
The two DC connection systems are not interchangeable. Images: Fronius International GmbH.
| Indications | Meaning |
|---|---|
| Charging LEDs are lit | SoC level: < 25 %, < 50 %, < 75 %, < 100 % |
| Flashes once per second | Battery loading |
| It flashes twice a second | Getting started o connecting to the inverter |
| Permanent power supply | Stable, achieved state |
You need to make a decision before buying equipment, because Only one variant can be implemented. They do not go together.
Two important restrictions:
For a Full Backup, the Backup Controller and the Fronius Backup Switch They allow for automatic or manual switching and are installed directly in the switchboard, without the need for an external switch box.
The purpose of switching is disconnect the property from the mains before operating in island mode. This is not just a regulatory whim: it prevents power from being supplied to a circuit that maintenance staff may be working on.
In normal operation, the disconnect contactors are closed and the house is connected to the grid.
When the power cut occurred, the power supply to the coils is automatically cut off. The contactors open, completely disconnecting the system from the mains supply. The feedback contacts change state; the inverter detects this and activates the backup relay, which keeps the contactors open. Thus, if the grid is suddenly restored, the system does not couple in parallel in an uncontrolled manner.
On the Symo GEN24 Plus, the switching time is less than 90 seconds, up to a maximum of 3,680 W per phase and a peak of up to 12,100 VA.
The control wiring is carried out using shielded cable 8-pole CAT5-7 (8 × 0.5 mm²), on the 16-pin connector of the investor.
If you’re using Windows 10: To enter the password, you must first click the link «Connect using a network security key instead». Otherwise, you won’t be able to type it in.
Menu settings Equipment configuration Only trained staff can carry them out: they require log in as the «Technician» user».
Updates can be found on the product page and in the Download Search section on fronius.com.
The battery is maintenance-free. Repairs are carried out only by specialist technical staff.
Cleanliness: A damp cloth if necessary. Never use cleaning products, abrasives or solvents.
And now for the most important piece of information in the manual, which almost nobody knows:
If the battery falls below its minimum charge level, it must be recharged within 7 days. Once this period has elapsed, the modules may suffer irreparable damage due to a complete discharge.
The forced reload Charging takes place automatically using solar or mains power when the minimum SoC is reached, provided that two conditions are met: the The DC isolator is in the «On» position» and the The inverter is connected to the mains.
This has a serious practical implication: if you leave the system switched off whilst you are away for a long period —a second home that is closed off in winter, a building site that has come to a standstill— and if the battery falls below the minimum level whilst the isolator is open, it cannot protect itself. Status messages appear on the inverter’s interface, and on Fronius Solar.web allows you to set up email alerts. Turn them on.
If the battery has switched off due to deep-discharge protection, it will not start on its own: you need to black screen on start-up by manually setting the DC isolator to «On». The same applies when starting emergency power mode following a power cut: the inverter requires power from the battery and this must be supplied manually.
Before working on the battery: All status LEDs must be completely switched off, and you have to wait for the inverter’s capacitors to discharge.
The entire system is monitored from Fronius Solar.web: solar generation, battery charging and discharging, and household consumption.
And there’s a feature that helps you get the most out of your battery if you’re on an index-linked tariff: the Fronius Energy Cost Assistant. Use AI to analyse your electricity generation, consumption and prices in order to charge the battery from the mains when the electricity tariff is low and use it when it goes up.
The Reserve is modular, comprising two levels: 2 to 5 modules inside the tower, preserving the BMS and the base, and up to 4 batteries in parallel.
However, the expansion has the same limitation as the initial installation: The Primo GEN24 Plus does not support versions higher than Reserva 9.5. If you’re planning to grow, that decision needs to be made when choosing an investor, not afterwards.
No. Fronius limits the Primo GEN24 Plus to the 6.3 and 9.5 configurations. For 12.6 or 15.8, you’ll need a Symo GEN24 Plus or a Verto Plus.
Yes. The meter provides the inverter with information on the property’s energy consumption and grid energy. Without it, surplus energy management and battery charging do not work properly.
No. Only one backup variant can be implemented per installation.
Yes. It stores energy and increases your self-consumption as normal. What it won’t do is power the house during a power cut.
This is the risk scenario. If the battery voltage falls below the minimum level and the isolator switch is open or the inverter is switched off, forced recharging cannot be carried out. If the modules remain below the minimum temperature for more than 7 days, they may suffer irreparable damage. Change your operating system and enable email notifications on Solar.web.
With the Symo GEN24 Plus, it takes less than 90 seconds to start up in stand-alone mode.
40 metres. And the communication cable: 30 metres at most, minimum CAT 5 shielded.
No. The installation must be carried out by an authorised installer, and the switchover to backup power must be agreed with the electricity supplier.
At FVComponents we are Fronius System Partner and Official Service Partner in Spain. If you’re sizing a system with a backup and want to check the inverter–battery–meter combination before buying, please get in touch and we’ll go through it with you.
You might also be interested in our Comparison between Fronius Reserva and Reserva PRO and the guide to batteries compatible with the Fronius GEN24 Plus.
Technical comparison between the Fronius Reserva and Reserva PRO, based on data from the official product specifications: capacities, compatibility with GEN24 Plus and Verto Plus, cost per kWh and selection criteria.
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