As seen on Open Homes Australia Season 4 and Australia’s Best House Season 3
As seen on Open Homes Australia Season 4 and Australia’s Best House Season 3
The Fronius Reserva is a high-voltage, DC-coupled home battery built to pair with the Fronius Primo GEN24 Plus and Symo GEN24 Plus hybrid inverters. It stacks from 2 to 5 battery modules of 3.15 kWh each, giving 6.31 to 15.79 kWh of usable storage per tower, and up to 4 towers can be connected in parallel.
If you already have a GEN24 Plus inverter, or you want a Fronius inverter with full three-phase backup, the Reserva is designed to complete that system.
Fronius is ISO 27001 certified and undergoes regular audits by leading cybersecurity firms, with all software developers trained in secure coding practices.
The Reserva only works with Fronius Primo GEN24 Plus (single-phase) and Symo GEN24 Plus (three-phase) hybrid inverters. If you have a different inverter, you would need to replace it or choose a different battery.
Each tower holds 2 to 5 battery modules of 3.15 kWh, giving 6.31 to 15.79 kWh of usable storage per tower. Up to 4 towers can be connected together, so you can grow your storage in small 3.15 kWh steps.
Yes. The Reserva supports backup power and black start, and paired with a Symo GEN24 Plus it can provide full three-phase backup. There is a short delay when it switches over to backup during a blackout.
Yes. It’s rated IP65 for water and dust and can go indoors or in a protected outdoor area. It operates from -20 to 55°C. In Brisbane we still recommend a shaded, sheltered spot, such as a south-facing wall under an eave, to keep it cool.
Fronius gives the Reserva a 10-year product warranty and guarantees it will keep at least 70% of its usable capacity over that period.
Fronius quotes 95% battery efficiency. In our own whole-system testing with a GEN24 Plus inverter, the Reserva achieved 90.2% round-trip efficiency in our fast test and 80.5% in our slow test, among the best results of any battery we’ve tested.
In our first year of installing it (November 2025 to July 2026), we installed Fronius Reserva systems for over 96 homes, made up of over 197 battery towers and over 814 battery modules, totalling over 2,570 kWh of storage.
Reviewed by Mark Cavanagh, owner of MC Electrical. Last updated October 2026.
Fronius Reserva is the battery we recommend for homes with a Fronius GEN24 Plus inverter, especially three-phase homes that want full-house backup. It expands in small 3.15 kWh steps, uses lithium iron phosphate (LFP) cells, and is rated IP65 for outdoor installation. The trade-off is that it only works with Fronius GEN24 Plus inverters, and blackout switching isn’t as instant as Powerwall 3.
Pros
Cons
In our first year of installing the Reserva (November 2025 to July 2026), MC Electrical installed:
The most popular size we installed was two 5-module towers (31.6 kWh), chosen by about a third of these homes. All installed by our own full-time electricians across Brisbane and South East Queensland. Source: MC Electrical job records, to July 2026.
A good fit if you:
Consider another option if you:
| Model | Specifications |
|---|---|
| 6.3 kWh | 6.31 kWh usable; 2 modules; 6.55 kW max charge/discharge; 890 x 772 x 176 mm; 86.5 kg |
| 9.5 kWh | 9.47 kWh usable; 3 modules; 9.83 kW; 1,140 x 772 x 176 mm; 120 kg |
| 12.6 kWh | 12.63 kWh usable; 4 modules; 13.10 kW; 1,390 x 772 x 176 mm; 153.5 kg |
| 15.8 kWh | 15.79 kWh usable; 5 modules; 16.38 kW; 1,640 x 772 x 176 mm; 187 kg |
| Module size | 3.15 kWh usable, 33.5 kg, 250 x 772 x 176 mm |
| Cell chemistry | Lithium iron phosphate (LFP), pouch cells |
| Depth of discharge | 94.5% |
| Battery efficiency | 95% (0.2C, 25°C) |
| Max output current | 32 A |
| Towers in parallel | Up to 4 |
| Compatible inverters | Fronius Primo GEN24 Plus and Symo GEN24 Plus |
| Water and dust rating | IP65; indoor or protected outdoor areas |
| Operating temperature | -20 to 55°C |
| Communication | RS485 |
| Certifications | IEC 62619:2022 (incl. thermal runaway test), VDE 2510-50, IEC 62477-1, UN 38.3, CE |
| Warranty | 10 years (70% state of health) |
Source: Fronius Reserva Australian datasheet. Last checked October 2026.
We measure round-trip efficiency ourselves: we charge each battery, discharge it, and log how much energy actually comes back out. High voltage batteries need only a small DC conversion; low voltage batteries need a large one, which costs more energy as heat.
| Battery type | Battery | Slow round trip1 | Fast round trip2 |
|---|---|---|---|
| High voltage | BYD | 81% | 89.4% |
| High voltage | Fronius Reserva (this page) | 80.5% | 90.2% |
| High voltage | Fox ESS (H3 Smart inverter + EQ4800 battery) | 73.84% | 86.6% |
| High voltage | SAJ | 79.9% | 89.0% |
| Low voltage | FranklinWH* | 81.3% | 87.8% |
| Low voltage | Tesla Powerwall 3 | 70.9% | 84% |
| Low voltage | Sigenergy | 62.9% | 80.3% |
| Low voltage | Anker | 65.4% | 80.5% |
| Low voltage | Huawei | 59.4% | 83.1% |
1 Slow test: charge at 100% of inverter capacity, discharge at 3% of inverter capacity.
2 Fast test: charge and discharge at the inverter’s maximum capacity.
* FranklinWH had an advantage with a 5 kW inverter, a 300 W discharge and a 6% discharge rate.
Fronius Reserva recorded the highest fast round-trip efficiency we’ve measured, at 90.2%, and 80.5% on the slow test. Fronius quotes 95% battery efficiency on its datasheet, measured at a lower 0.2C rate.
Every battery in this table is tested the same way, at our warehouse test facility or on a real home install. We charge the battery, discharge it, and use a power logger to measure the energy going in and the energy coming back out. Round-trip efficiency is the energy out divided by the energy in, so it shows how much of your stored solar you actually get to use. For example, a battery with 73% round-trip efficiency gives you back about 7.3 kWh for every 10 kWh you put in.
We run two tests on each battery:
Why the battery type column matters: batteries store DC (direct current) electricity, and your home runs on AC (alternating current). High voltage batteries only need a small DC-to-DC conversion before the inverter turns it into AC. Low voltage batteries need a much bigger conversion, and every conversion loses some energy as heat. Many low voltage batteries also have a DC-to-DC converter inside every battery module. Each converter has a running cost, a bit like a car engine idling, whether you’re using much power or not. In our testing that was roughly 70 W per module. On a big stack running a small night-time load, those running costs add up, a bit like leaving a bathroom heat lamp on 24 hours a day. That’s why the high voltage batteries in our table generally score higher, especially in the slow test.
We say so when we get it wrong: while testing a large modular battery in 2026, we found that setting the slow test by inverter size alone didn’t tell the whole story for batteries with a converter in every module. What matters is how much power each module is handling. A six-module stack discharged at 300 W came out in the low 40s for round-trip efficiency, while the same stack at 900 W came out at about 67%. We published what we found, and it changed our advice: choose a battery sized to your home rather than the biggest stack you can fit.
Keeping it fair: where a system could not be tested at exactly the same rate as the others, we mark it with an asterisk and explain why. For example, the FranklinWH result has an asterisk because its 5 kW inverter meant our 300 W load worked out to a 6% discharge rate instead of 3%, which gave it an advantage in the slow test.
Independent results: manufacturers sometimes help with the cost of a test unit or travel, but they never get a say in what we publish. We’ve turned down reviews when a brand wanted that kind of influence.
Only systems we’ve tested ourselves: every result comes from a system we installed and measured. If the exact model on a page has not been tested yet, we say which model we did test.
Testing at both ends shows how a battery performs in a real home, not just the best-case figure on a datasheet. Manufacturer efficiency figures are often measured on the battery alone, which is one reason our whole-system results are lower.
Source: MC Electrical in-house round-trip efficiency testing, 2026.
Model | Usable Capacity | Modules | Voltage Range | Dimensions (H×W×D) | Weight |
Reserva 6.3 | 6.31 kWh | 2 | 185.6–227.2 V | 860×780×176 mm | 86.6 kg |
Reserva 9.5 | 9.47 kWh | 3 | 278.4–340.8 V | 1100×780×176 mm | 120 kg |
Reserva 12.6 | 12.63 kWh | 4 | 371.2–454.4 V | 1360×780×176 mm | 153.5 kg |
Reserva 15.8 | 15.79 kWh | 5 | 464–568 V | 1610×780×176 mm | 187 kg |
Battery type: Lithium Iron Phosphate (LFP)
Protection rating: IP65 – suitable for indoors or protected outdoor areas
Operating temp: -20°C to +55°C
Monitoring: Fully integrated with Fronius Solar.web
Warranty: 10 years.
“Longevity is particularly important to us at Fronius. We therefore guarantee that the Fronius Reserva will still deliver at least 70 percent of its usable energy after ten years from the start of the warranty.”
| Tesla Powerwall 3 | Fronius Reserva (with GEN24 Plus) | Fox ESS Power Cube | |
|---|---|---|---|
| Usable capacity | 13.5 kWh per unit | 6.31, 9.47, 12.63 or 15.79 kWh per tower (2 to 5 modules of 3.15 kWh) | 10.92 to 49.14 kWh (2 to 9 EQ5500 modules of 5.46 kWh) |
| Expanding later | Add up to 3 Powerwall 3 Expansions (13.5 kWh each) per Powerwall 3 | Add modules to a tower (up to 5), or up to 4 towers in parallel | Add EQ5500 modules (up to 9) |
| Inverter | Built in | Separate Fronius Primo or Symo GEN24 Plus hybrid inverter | Built in |
| Inverter sizes | 5, 10 or 11.04 kW continuous | Set by the GEN24 Plus inverter chosen | 5, 8, 10 or 12 kW single-phase; 5 to 15 kW three-phase |
| Solar input | Up to 20 kW DC, 3 MPPTs | Set by the GEN24 Plus inverter chosen | Up to 200% of inverter rating, 4 MPPTs (2 on the 5 kW single-phase model) |
| Efficiency (manufacturer) | 89% solar to battery to home; 97.5% solar to home | 95% battery efficiency | Battery round trip greater than 95% |
| Water and dust rating | IP55 enclosure; IP67 battery and electronics | IP65 | IP65 |
| Weight | 130 kg (Expansion 110 kg) | 86.5 kg (6.31 kWh) to 187 kg (15.79 kWh) | Inverter 35 kg plus battery modules |
| Operating temperature | -20 to 50°C (may derate above 40°C) | -20 to 55°C | Inverter -25 to 60°C; battery charges 0 to 55°C |
| Cell chemistry | Not stated on datasheet | Lithium iron phosphate (LFP) | Lithium iron phosphate (LFP) |
| Warranty | 10 years | 10 years (to 70% state of health) | 10 years |
| Status at MC Electrical | Available now | Available now | Awaiting Clean Energy Council (CEC) approval |
Figures are taken from each manufacturer’s current Australian datasheet. Last checked October 2026.
At MC Electrical, we only install what we’d use on our own homes. Our team has hands-on experience with all three systems – and we’re here to help you find the right solution.
Contact us today to get a personalised solar battery recommendation.
Mark Cavanagh is the owner of MC Electrical. He started his career as a 16-year-old apprentice electrician at Energex, then worked in residential and commercial electrical before completing his first solar install in 2009.
In 2012, frustrated that nobody had real, comparative data on solar products, Mark started buying and testing panels, inverters and batteries himself at our warehouse test facility and publishing the results on Mark’s Blog. That testing has since earned invitations to inverter and battery factories to sit down with the engineers behind the products, minus the sales spin.
Today Mark presents battery reviews on the MC Electrical YouTube channel with solar consultant Yorick Mark. In one two-year period alone, they made four trips to China and visited seven battery manufacturers, then installed and tested the most promising systems side by side. Manufacturers sometimes help with the cost of a test unit or flights, but Mark’s rule is that they get no say in what is published, and he has turned down reviews when a brand wanted that influence. He lives with the technology too: his own home runs a 15 kW Fronius inverter with 48 kWh of battery storage.
Under Mark, MC Electrical has installed over 14,000 solar systems of various brands, including over 5,590 Fronius inverters, and has teams installing over a thousand solar systems a year. MC Electrical is a Tesla Powerwall Certified Installer, a Master Electricians member and an NETCC Approved Retailer, and every installer is a full-time employee, never a subcontractor.
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