Fronius Reserva Battery and GEN24 Inverters

The Fronius Reserva is a high-voltage home battery made by an Austrian, family-owned inverter manufacturer, and it is designed to work with the company's own hybrid inverters rather than as a standalone unit¹. Storage runs from 6.3 to 15.8 kWh in a single tower, built up in 3.15 kWh modules, and a GEN24 Plus inverter can support up to 63 kWh across four towers in parallel¹.

For a household, the practical questions are whether an existing Fronius inverter can take a battery, what the system keeps running in a power cut, and what it costs. The answers are mostly favourable: the Reserva is compatible with the Primo GEN24 Plus, Symo GEN24 Plus and Verto Plus families, carries a ten year warranty, and can be retrofitted to a GEN24 that was installed without storage³.

The dependence it leaves is the usual one for a hybrid system. The battery stores and shifts energy, but the household still draws from the grid when the sun is down and the battery is empty, still buys that power from a supplier, and still relies on a manufacturer's app and firmware for monitoring and for the newest backup features.

Fronius: an Austrian, family-owned inverter maker

Fronius is a family-owned enterprise, and it makes photovoltaic systems for homes and businesses⁷. More than 90% of its products are manufactured in Austria, and the company states that 100% green power is used at its production facilities there⁹. One Austrian production site runs on PV systems with a total output of 4.2 MW and is cooled in summer by an ice storage facility with an output of 6.3 MW¹⁰.

That manufacturing base matters for a household in a quiet way. A European supply chain shortens the distance a replacement part travels, and the company's own statement that inverters are produced in compliance with strict quality guidelines in Europe is a claim about process rather than a guarantee of performance⁹. Fronius inverters with active cooling are described as basically maintenance-free, which is the maker's position on servicing rather than an independent finding¹¹.

The company's product line is broader than storage. It covers inverters, batteries, backup power and e-mobility, and the Reserva sits inside that ecosystem rather than beside it⁷. That is the central fact about buying one: the battery is not a generic box that will pair with any inverter, and Fronius states plainly that the Reserva has been specially developed for its hybrid inverters².

For energy independence, the maker's nationality and ownership change little day to day. What it does change is where the warranty is honoured, where spares come from, and how long the product line is likely to be supported. A household buying into a single maker's ecosystem is trading some flexibility for tighter integration, and that trade is worth naming rather than glossing over.

Reserva at a glance: 6.3 to 15.8 kWh of storage

The Reserva is sold in fixed capacities rather than as a free-form stack. Fronius lists usable capacities of 6.31 kWh for the Reserva 6.3, 9.47 kWh for the 9.5, 12.63 kWh for the 12.6 and 15.79 kWh for the 15.8¹. The warranty document gives the same figures as usable energy for country group 1, which includes the UK³.

Each module contributes 3.15 kWh of usable capacity, and the system can be expanded at any time in those increments up to 15.8 kWh per battery tower¹. Up to four batteries can run in parallel, which is how the 63 kWh maximum is reached in combination with a GEN24 Plus¹.

The Reserva Pro range is larger and runs on the same modular principle.

Those throughput figures are the warranty's measure of how much energy the battery is expected to pass through over its life, and they are the number to compare against a household's annual consumption rather than the headline kWh. The warranty is written around cycle life, not calendar life alone. More on how capacity and throughput interact is at battery capacity and usable capacity and battery cycle life and degradation.

Which inverter pairs with which Reserva

The Reserva is a high-voltage battery for Fronius hybrid inverters, and the compatibility list is specific. Fronius states that the Reserva is compatible with its hybrid inverters except the Fronius Symo Hybrid, and the datasheet names the Primo GEN24 Plus, Symo GEN24 Plus and Verto Plus¹.

The model-level list narrows it further. The Reserva 6.3 and 9.5 work with the Primo GEN24 Plus, Primo GEN24 Plus SC, Symo GEN24 Plus, Symo GEN24 Plus SC, Symo Hybrid and Verto Plus. The Reserva 12.6 works with the Primo GEN24 Plus SC, Symo GEN24 Plus, Symo GEN24 Plus SC and Symo Hybrid. The Reserva 15.8 works with the Symo GEN24 Plus, Symo GEN24 Plus SC and Symo Hybrid¹².

The GEN24 Plus family is described as versatile hybrid inverters that allow battery storage and customised backup power solutions to be integrated⁵.

A household that already has a GEN24 without the Plus designation is not locked out. Fronius offers the UP.storage software upgrade, which retrofits a battery connection at any time, including the full backup option². That upgrade is available in the Fronius webshop in selected countries, so availability is worth confirming locally¹³. The wider question of how AC and DC coupling differ is covered at AC-coupled and DC-coupled battery systems.

Backup power and black start: what Reserva with a GEN24 Plus keeps running

Backup is where the Fronius system earns its place for a household worried about outages. Fronius states that a combination of backup power and black-start capability in the hybrid inverter and battery enables the system to reactivate itself automatically, even without power from the grid⁵. The Reserva is described as capable of providing backup power and black start capability¹⁴.

The scale of that backup depends on the switching equipment. Fronius states that full backup for the entire household requires the battery together with a GEN24 Plus or Verto Plus and switching components such as the Fronius Backup Controller or Backup Switch¹. With those in place, Fronius describes full backup as able to supply the whole home, including large loads such as heat pumps¹⁵.

There are two levels. Full backup and the battery function are only available with the GEN24 Plus version of the inverter, not the standard GEN24¹⁶.

Black start is the part that matters most in a long outage. A system that can restart itself without the grid can keep running through a wider area failure, rather than waiting for the network to come back before it will operate. Fronius describes the GEN24 Plus and Verto Plus hybrid inverters and the Reserva as boasting these features, making a household truly self-sufficient in its home⁵.

What remains outside the household's control is the grid connection itself. Backup covers the circuits wired into the backup supply, and the system still needs the battery to hold charge when the outage begins. A household that empties the battery on a normal evening has less in reserve when the power fails at midnight. The mechanics of changeover and what typically stays on are set out at battery backup in a power cut.

Warranty: ten years under Fronius Warranty Plus for UK installations

The Reserva warranty period is ten years, unless otherwise stipulated, and it covers the Reserva BMS and the Reserva Module³. The Reserva Pro terms are stated as ten years at 80% state of health³. The German-language datasheet for the Reserva gives the same ten year figure⁴.

The start date is the detail most householders miss. Fronius states that the warranty period begins six months after initial delivery from Fronius, not on the day the installer commissions the system³. That gives a little extra cover at the front end, and it means the paperwork to keep is the delivery record rather than the handover date.

The current terms apply to covered products purchased on or after 1 March 2026, so a Reserva bought before that date sits under earlier conditions³. The UK falls into country group 1 in the warranty document, which is the group that carries the ten year period for the battery³.

Inverter cover runs alongside it. Fronius inverters from 0 to 49 kW in country group 1 carry ten years in total, made up of five years of Fronius Warranty Plus and five years of Fronius Warranty thereafter¹⁸. Registration at solarweb.com within thirty months of delivery ex works secures the free extension, and Fronius states that registering secures ten years of free and reliable warranty cover for inverters under 50 kW¹⁸. Inverters of 50 kW and above get five years of free cover on registration, and a paid extension can take cover up to 15 years¹⁹.

The base position, where no longer period applies by country, is two years¹⁸. The documents also disagree on the free extension for smaller inverters, with one Fronius page giving up to 10 years and another giving 5 years for inverters under 50 kW; the ten year total in the warranty terms is the figure tied to country group 1¹⁹. How retained capacity and throughput conditions compare across makers is at home battery warranties.

Installation, siting and commissioning

The Reserva carries an IP65 protection class, and Fronius gives the installation location as indoors and protected outdoor areas¹. Protected outdoor siting means a position sheltered from direct weather rather than an exposed wall, so a garage, plant room or covered outbuilding fits the description.

The operating ambient temperature range is minus 20 to plus 55 degrees C, and Fronius notes that charging and discharging power may be limited depending on temperature¹. That is a performance note rather than a safety limit: the battery keeps working across the range, but it will not necessarily deliver full power at the extremes. Ventilation and temperature behaviour in general is covered at ventilation, temperature and operating conditions.

Commissioning runs through the Solar.start app, and Fronius states it needs no additional software¹. The installer pairs the battery with the hybrid inverter and brings the system online during the visit. Monitoring afterwards sits in Fronius Solar.web, which Fronius describes as one app covering the system¹.

Firmware is part of the picture. Fronius released GEN24 bundles through 2026: 1.40.8-1 on 15 April, 1.40.9-1 on 20 May, 1.41.10-1 on 13 July and 1.41.11-1 on 10 August. The July bundle added parallel backup operation and uninterruptible backup changeover, and the May bundle carried third-party software library updates addressing listed CVEs. The August bundle fixed the Italy autotest, German NA protection configuration and false triggering of an AC bridge fault. Keeping the inverter updated is therefore not cosmetic: some backup features arrived by firmware rather than at the factory.

Availability and pricing in the UK, and what owning a Reserva means for independence

Fronius states that the Reserva warranty is geographically limited to the countries specified in its terms, and the United Kingdom sits in country group 1, which is the group carrying the ten year battery period³. The Reserva Pro is described as developed and manufactured in Europe.

On price, the figures available are distributor listings rather than a manufacturer list price. One UK distributor lists the Reserva from £1,021.88 and the Reserva Pro from £1,162.39, with the Reserva Pro BMS and base at £1,162.39⁶. Those are equipment prices from a single seller and should be read as indicative; installation, mounting, switching components and commissioning are quoted separately by the installer, and no published installed price exists for a Fronius system in the UK.

The UP.storage retrofit upgrade is available in the Fronius webshop in selected countries, so a household wanting to add storage to an existing GEN24 should confirm UK availability before planning around it¹³.

What the system does for independence is real but bounded. The battery shifts solar generation into the evening, the backup function keeps selected circuits running through an outage, and black start means the system can come back without the grid⁵. What it does not do is remove the grid connection, the electricity supplier or the gas supply if the home heats with gas. The household still buys power when the battery is empty, still depends on the network for the periods the battery cannot cover, and depends on Fronius for firmware, the Solar.web platform and the app that shows what the system is doing. A household that wants to understand where that leaves it should read home batteries and household energy independence and monitoring a home battery.