How to judge a solar battery brand: eight checks before you pay more

A dearer battery brand is worth the money when you can point to the reason on a document. Brochures rank brands. Datasheets, warranty PDFs and two public lists let you check them. Anyone working out how to choose a solar battery brand can run eight checks before signing a quote, each with a place to verify it. Figures, document revisions and list statuses are as at 25 September 2026.

Usable capacity, the energy you can draw out of a battery in kilowatt-hours, is the figure every check below relies on. The cells hold more than that. Rebates and warranties are written against the usable number.

The GoodWe ESA and the Sigenergy SigenStor appear throughout because both publish every document the checks need.

What are the eight checks?

Usable capacity, the warranty, the two lists, the company behind the warranty, backup, efficiency, offline behaviour and years in Australia, in the order you meet them on a quote.

Checks 1 to 5 take an evening. Open the quote, the datasheet and the warranty side by side and work down the table.

How much of the battery can you use?

Less than the total on the brochure: the usable figure on the datasheet, measured under the conditions in its footnote. All makers test new batteries at about 25°C, charged and emptied slowly. GoodWe's footnote for its 5.1 kWh module reads 98% depth of discharge, a 0.2P rate, 25°C, beginning of life; depth of discharge is the share of the total the maker lets you use. Sigenergy's is close: 100% depth of discharge, 0.2C, 25°C, beginning of life. Tesla prints only 25°C and beginning of life. A north-facing garage wall in Ellenbrook in February is not 25°C, and neither is one anywhere else in Perth, so the figure is a ceiling rather than a promise.

Even official documents disagree. The Clean Energy Council register lists GoodWe's 6 kWh module at 5.9 kWh usable and its 9 kWh module at 8.85 kWh; GoodWe's own September 2026 datasheet prints 5.8 and 8.7. Sigenergy's newer modules show the same pattern: the register carries 6 and 9 kWh usable where the datasheet prints 5.84 and 8.76 and the warranty uses 6.0 and 9.0. The gaps are small, but they decide which figure the rebate is calculated on, so ask the installer which document the quote used.

Cycle ratings are not comparable across brands. GoodWe qualifies its 8,000 and 10,000 cycle figures as "specific laboratory conditions" with no temperature or rate given. Sigenergy publishes 10,000 cycles for its BAT 6.0 and 10.0 modules as the cell maker's figure at 25°C, half-rate charging, down to 60% health, and publishes no cycle figure at all for the BAT 5.0 and 8.0. Neither figure is a warranty term.

Both rebates use the usable figure. The WA Residential Battery Scheme pays Synergy customers $130 per usable kWh, capped at $1,300, which lands at 10.0 kWh usable. The federal program creates certificates on the first 50 kWh of usable capacity and asks for at least 5 kWh of nominal capacity per battery, the total figure on the datasheet rather than the usable one. Two GoodWe GW5.1 modules give 10.0 kWh usable and two Sigenergy BAT 5.0 modules give 10.4 kWh. Either reaches the WA cap.

What does the warranty promise?

Read a 10-year battery warranty for its numbers first and its clauses second. The numbers are the term in years, the share of usable capacity the battery must still hold at the end, and the cap on total energy moved before the cover ends early; the clauses cover offline periods, coastal sites and claim deadlines. How battery warranties work explains the skeleton; the battery warranty comparison lines up the brands sold here.

Throughput is where 10 years can mean eight. GoodWe's 3.0 MWh per usable kWh equals 3,000 full cycles; a battery emptied and refilled every day reaches that in a little over eight years, and GoodWe's text says the cover is sized for one full cycle a day. Sigenergy's cap on the 5.2 kWh module works out to about 3,800 full cycles, a little over ten years at the same pace. Few homes run a full cycle every day of the year, so the cap usually sits behind the 10-year term, but a large solar array feeding a small battery can change that. Tesla structures the same idea differently: unlimited cycles for solar self-consumption and backup, and a 37.8 MWh cap for any other use.

Read the clauses before the price.

Connection. Sigenergy's cover depends on the system staying online for firmware updates. Ninety days offline puts it into a safe operation mode; a year offline shortens the warranty to five years from activation. Tesla's Australian warranty says an unconnected or unregistered Powerwall may not receive the full ten years, with a floor of four. GoodWe's battery warranty has no connection clause.

Coast. GoodWe excludes damage from sea coasts or saltwater unless GoodWe approved the installation in writing beforehand. For a home in Scarborough, Fremantle, Rockingham or any other suburb near the coastline, get that approval before the install; a claim is too late. Sigenergy's current warranty has no distance clause; an earlier version excluded installs within 500 metres of the coast, so check the date on the document you are handed.

Claim windows. GoodWe wants a fault reported within two weeks and a claim lodged within a month. Sigenergy wants the claim within 30 days, lodged through its app. Both treat a late claim as abandoned.

Model list. GoodWe's current battery warranty names the G20 module codes; the datasheet and the Clean Energy Council register also carry G21 versions of the 5.1 and 8.3 kWh modules. A quote carrying a G21 code needs a warranty document that names that code, and the current one does not. Sigenergy's names every configuration from the 3S to the 30T.

Is the model on both lists that matter in WA?

Only a search by model number can tell you, and a brand name on its own proves nothing.

Start with the Clean Energy Council's approved battery list, which holds the products assessed against its battery safety guide; its approved inverter list does the same for inverters. Government rebate programs require systems to use products from these lists, and the federal program will not create certificates for a battery that is missing from it. Each entry shows an approval date, an expiry date, the total and usable capacity, and the compliance pathway. Standards Australia released a new technical specification in October 2025, SA TS 5398, which the Council is adopting in place of its guide, so the pathway column is changing. Listing is by model number. GoodWe's 6 and 9 kWh modules were added in July 2026, eleven months after its 5 and 8 kWh modules. The SigenStor configurations built on the newer 6.0 and 10.0 modules arrived in April 2026, 22 months after the first SigenStor listings.

Synergy's Supported Solutions List is the WA gate, covered in depth in how Synergy's list works. It lists inverters and the software clients that manage them. A battery system qualifies for the WA rebate and for Synergy Battery Rewards through the inverter row it sits behind, under DER-Storage, the list's heading for battery systems. DER means distributed energy resources. Each category has a Provisional column and a Full Listing column, and some rows carry a green tick. The list defines the tick: the solution is ready to be activated under a VPP program. Nowhere does it define the two columns. It does state that every DER-Storage listing meets the scheme's technical requirements and is progressing toward activation readiness.

As at 25 September 2026, all 15 GoodWe ESA inverter rows and all 836 SigenStor rows sat in the Provisional column, and none carried the tick. A minority of rows across the whole list already do. Joining a virtual power plant is a condition of the WA rebate, and Battery Rewards is the Synergy program that satisfies it, so what the missing tick means for your activation date is a question to put to Synergy or the installer before you sign. The WA rebate eligibility checklist covers the rest of the paperwork.

Who in Australia stands behind the warranty?

The company named on the last page of the warranty PDF stands behind it. That page should name an Australian entity, give a street address and tell you how to lodge a claim. GoodWe's names GoodWe Australia Pty Ltd in Rowville, Victoria, and routes claims through the installer or distributor first, then GoodWe's service portal. Sigenergy's names Sigenergy Australia Pty Ltd in North Sydney; claims go through the mySigen app. Tesla's warrantor is Tesla Motors Netherlands B.V., with an Alexandria, New South Wales address for claims and the certified installer as the first contact.

Who you can hold to what depends on that name. Under Australian Consumer Law, the business that sold you the system must fix problems with it. It cannot send you to the maker instead, though for some guarantees you can choose to go to the manufacturer. Where the maker has no place of business in Australia, the law treats the importer as the manufacturer, which is why the importer's name on that last page is the one that counts. Consumer guarantees apply automatically and no warranty document can remove them; a warranty is an extra promise on top. Making a battery warranty claim walks through the process.

Find the support email or portal on that page and check it belongs to the Australian entity. GoodWe's page lists an Australian service address. Sigenergy's lists a global address as well as an Australian one.

How does the backup work, and is it on the quote?

Backup is either inside the inverter or in a separate box, and the quote should show which. The GoodWe ESA has it inside: a 63 A bypass on the single-phase inverter and 80 A on three-phase, so no separate gateway is needed. Whether that covers the whole house still depends on the inverter's rated backup output for the size on your quote, so check that row on the datasheet as well. The SigenStor delivers backup through the Sigen Energy Gateway, a separate wall unit between the grid and the house; Sigenergy's gateway datasheet says the 0 ms changeover is achieved with the gateway, controller and battery working together, and without the gateway there is no backup function. Tesla's Powerwall 3 lists the Backup Gateway 2 as its islanding device, also a separate unit.

A quote for a gateway-based system that does not itemise the gateway is a quote without backup. How much of the house to back up is a separate decision, covered in whole-home vs essential backup and what happens in a blackout.

Which efficiency figure is on the datasheet?

Usually it is an inverter figure. The whole round trip is rarely printed, and makers publish different measurements under similar labels, which makes efficiency the least comparable number in this market. Round-trip efficiency measures what comes back out of the battery at the AC side after a full charge and discharge, counting the charging conversion, the battery's own losses and the discharge conversion. An inverter's maximum efficiency counts one conversion, one way.

The gap between 98% and 89% comes from measuring one conversion against the whole path, and says nothing about hardware quality. Tesla's 89% is the only whole-path figure among the four, so it is the only one you could hold a real bill against. There is no Australian standard test behind the term, so makers choose what to publish. Treat any single efficiency percentage on a quote as an inverter number unless the datasheet says otherwise, and put more weight on usable capacity and warranty terms, which are written into documents you can enforce.

What happens when the app or the internet goes away?

Sigenergy's system slows itself after 90 days offline, Tesla expects a connection, and GoodWe's warranty says nothing about it. New battery systems in WA are expected to be online. Under the WA connection rules from 1 May 2026, new or upgraded solar and battery systems up to 30 kVA must support the grid communication standard Synergy uses to commission them, and must be able to be turned down or off remotely in an emergency. Battery Rewards credits also require a reliable internet connection at the home, so the WA scheme itself assumes the system is online. The brand check is what the maker does when the link drops.

Sigenergy publishes the answer in a technical note. After 90 consecutive days without a cloud connection the system enters a safe operation mode. Charging and discharging drops to 70% of rated power outside a 10 to 45°C cell temperature band. The usable range narrows to between 10% and 90% of capacity. Most automatic operating modes switch off and software updates stop until the link comes back, at which point full function returns. Tesla's datasheet says the customer is expected to provide internet connectivity, and Tesla's support pages describe the offline fallback as local monitoring from a phone on the same network, on recent firmware. GoodWe's help pages say a lost Wi-Fi link does not stop the inverter producing and exporting, and neither its help centre nor the ESA manual says how the battery behaves offline.

Firmware can also gate a specification: Tesla's Australian datasheet says a higher charge rate with expansion units will arrive with a future firmware version, so a figure on a datasheet can depend on an update that has not shipped.

How long has the brand been selling here?

GoodWe has been here since 2012, Sigenergy's Australian warranty covers installs from November 2023, and the spare-parts guarantee under consumer law applies to both regardless. A 10-year warranty is a bet on the company as much as the product. GoodWe was founded in 2010 and says it set up in Australia in 2012; its ESA is new, with single-phase units launched in October 2025. Sigenergy was founded in 2022; its Australian warranty covers systems installed from November 2023, and its first SigenStor configurations reached the Clean Energy Council list in June 2024. The dates settle nothing on their own. A new maker can carry a strong balance sheet and an established one can leave a market.

Spare parts have their own guarantee. Australian Consumer Law requires the manufacturer, or the importer standing in for it, to take reasonable action to keep repair facilities and spare parts reasonably available for a reasonable period after purchase. "Reasonable" is not defined in years. For a modular battery, ask where a replacement module would come from in year seven. Each company's record is covered in the GoodWe review, the Sigenergy review and the Tesla review; brand reliability factors goes further on tenure and local presence.

How do the eight checks land on the two examples?

The two products match on the warranty numbers and the list status, and part company on backup, offline behaviour and the coastal clause.

The battery comparison guide covers the wider set of buying factors for these two and for other brands.

What should you ask before paying more for a brand?

Ask for the documents behind each answer below.

• The exact inverter and module model numbers on the quote, checked against both Clean Energy Council lists and Synergy's list on the day you sign.
• The usable-capacity figure the rebate was calculated on, and its source document.
• The warranty document by revision and date, and whether it names the module codes on your quote rather than only the brand.
• The throughput or cycle cap, in years at one full cycle a day.
• The connection clause, and what happens after 90 days offline.
• For a coastal address, the maker's written approval before installation where the warranty asks for it, filed with the quote.
• Backup: inside the inverter, or a gateway with its own line on the quote.
• Which efficiency figure the quote cites, which row of the datasheet it came from, and whether it is a whole-path figure.
• The Australian entity on the warranty, and the claim channel.
• Where a replacement module would come from in year seven, who ships it, and how long that takes.

Frequently asked questions

Is a dearer solar battery brand worth paying for? Only where one of the eight checks shows a difference you can read on a document: a higher throughput cap, backup without a gateway, a whole-path efficiency figure, a longer Australian record. A higher price with matching usable capacity, end point and list status is only a price difference.

Does the WA rebate depend on the battery brand? No. The model numbers decide it. The battery and inverter need to be on the Clean Energy Council lists and the system under DER-Storage on Synergy's Supported Solutions List. The install also has to be done by an accredited installer who is a Synergy-registered equipment retailer, pass commissioning, and come with a virtual power plant commitment. Any two brands that both pass receive the same $130 per usable kWh, capped at $1,300, however far apart their prices sit.

What does a provisional listing on Synergy's list mean? Synergy's list leaves the word undefined, and states only that every DER-Storage listing meets the scheme's technical requirements and is progressing toward activation. If your quoted model has no tick, ask Synergy or the installer when activation in Battery Rewards is expected.

Is a 10-year warranty the same from every brand? No. GoodWe's ends at 70% capacity or 3.0 MWh per kWh, Sigenergy's at 70% or about 3.8 MWh per kWh, and Tesla's runs to unlimited cycles for self-consumption. Sigenergy's shortens to five years after a year offline and Tesla's to four; GoodWe's has no such clause. Read the end percentage together with the cap and the clauses.

Where next

Where to place a battery in a Perth home

AS/NZS 5139 clearance rules, garage vs outdoor walls, and what installers check on-site.

How to size a battery for your usage

A step-by-step method covering evening usage and seasonal AC demand.

Synergy Battery Rewards: what the VPP pays

Activation events credit 70¢/kWh on top of DEBS exports, and signing up is a WA rebate condition.

Explore your options

Answer a few questions and see systems and installers that fit your home.