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Detailed reviews and information of the best solar panels, inverters and batteries. Plus hybrid and off-grid solar system reviews and information articles on how solar and battery systems work.


Reviews and information on the best Solar panels, inverters and batteries from SMA, Fronius, SunPower, SolaX, Q Cells, Trina, Jinko, Selectronic, Tesla Powerwall, ABB. Plus hybrid inverters, battery sizing, Lithium-ion and lead-acid batteries, off-grid and on-grid power systems.

Tesla Powerwall 2 Vs LG chem RESU Vs Sonnen ECO Vs BYD

Jason Svarc


We compare the leading AC batteries from Tesla and Sonnen against the popular DC coupled batteries from LG chem and BYD. A direct comparison is not easy as each battery type has various advantages and disadvanatges, depending on the application and amount of storage capacity required. Other factors include the location (indoors or outdoors) and whether the battery is retrofitted to a home with an existing solar system. The full battery comparison criteria is explained in detail in the complete solar battery review.

AC coupled batteries

Tesla Powerwall 2 and Sonnen ECO

Both the Tesla Powerwall 2 and Sonnen ECO are AC batteries, meaning they have integrated battery inverters and are connected via AC coupling. These battery systems also require an additional solar inverter to operate with a solar array. One of the most significant benefits of AC batteries is that they can be retrofitted to any home with an existing solar installation. Batteries can also be retrofitted via AC coupling inverters such as the SMA Sunny Boy Storage, but here we will focus on the two popular AC battery options.

One of the disadvantages of AC coupled batteries is the slightly lower efficiency. The ‘round trip’ efficiency (charging and discharging loses) of AC batteries is around 90%, while most DC batteries average 96%. These additional loses are due to the multiple power conversions; first the solar inverter converts the DC solar power to AC, then the battery inverter converts from AC to DC during charging, and finally back to AC when the battery is discharged. However, these additional losses are a relatively small compromise.

A basic layout diagram of an AC battery storage system - More information in the  AC vs DC coupled review

A basic layout diagram of an AC battery storage system - More information in the AC vs DC coupled review

The Tesla Powerwall 2 is the only liquid-cooled battery on the market, which gives it a wide operating temperature range (-20 to 50 degC) and is less likely to derate (reduce output) in both high ambient temperatures and extremely low temperatures. Furthermore, it has a very high weather rating (IP56), meaning it can safely be installed outside. However, as with any battery system, it is always wise to install it in a sheltered location and out of direct sunlight. The Sonnen ECO on the other, hand has a low (IP20) weather rating and cannot be installed outside unless a special enclosure is used which adds to the cost. In regards to storage capacity, the Powerwall 2 is only available in the one 13.2kWh size, while the Sonnen ECO is a modular system with multiple options from 3.3 to 16 kWh.

Battery life and power ratings

In terms of life span and warranty, the Sonnen ECO battery uses longer life Lithium LFP (Lithium Ferro Phosphate) battery cells and comes with one of the best warranties on the market, with an estimated 88% retained capacity after 10 years. The Powerwall 2, on the other hand, uses Lithium NMC cells similar to those used in the electric vehicles, with an estimated minimum 70% retained capacity after 10 years. Although in regards to power output, the lithium NMC batteries used by Tesla have a higher discharge rate which equates to higher power output at 5kW continuous, compared to a maximum of 3kW power rating from the Sonnen ECO.

Battery power rating comparison chart. Note: BYD rating for 2 x 2.56kWh modules

Battery power rating comparison chart. Note: BYD rating for 2 x 2.56kWh modules

DC coupled Batteries

LG chem RESU and BYD B-Box

Both the LG chem RESU and BYD B-Box are DC coupled batteries. These Lithium battery systems are designed to be used with a compatible hybrid inverter for grid-tie systems, or more powerful multi-mode inverter for off-grid installations. Compared to the relatively small number of AC battery options on the market, the many DC batteries are compatible with a wide range of popular hybrid and multi-mode inverters such as the SolarEdge StorEdge inverters, Sungrow hybrid, Huawei hybrid, Solax hybrid and the powerful off-grid inverters from Victron Energy and Selectronic. Having a wide range of inverter options means the DC battery systems can be configured to suit a large variety of different solar installations, from simple economical self-use systems to more powerful off-grid installations with backup for high load appliances.

Basic DC coupled battery system diagram with a common hybrid inverter plus backup AC output.

Battery life and power rating

While the LG chem and BYD B-Box are both DC coupled batteries, they have several important differences including cell chemistry, design and configuration options. The BYD B-Box is a modular system comprised of multiple smaller capacity 2.56kWh battery modules. The LG chem batteries, on the other hand are much larger single battery modules. A key difference is LG chem use Lithium MNC pouch cells, while the BYD uses the more common Lithium LFP cylindrical cells. Despite these differences, both batteries have very similar performance characteristics and expected lifespan which is highlighted in the detailed complete solar battery review.

The biggest difference between the two DC battery options is the LG Chem RESU10 is limited to 5kW continuous power output (even with multiple batteries connected in parallel), while BYD is infinitely scalable to deliver much higher continuous and peak power. The 5kW limitation of the LG chem is generally only an issue for home with very larger power requirements or off-grid systems.

Tesla Powerwall 2

AC Coupled Battery

Image Credit: Tesla energy

Image Credit: Tesla energy

The Tesla Powerwall 2 with 13.5kWh of 'usable' storage capacity is an AC battery as it comes with an integrated 5kW DC-AC inverter/charger. AC batteries can be fitted to home with existing solar installations which can make installation simplier, but still require a solar inverter to function with a solar array, plus the additional Tesla gateway box is required to enable backup power (UPS) during a grid outage.

The Powerwall 2 uses a lithium nickel-manganese-cobalt (NMC) cell chemistry developed in collaboration with Panasonic as the battery cells are similar to the batteries used in the Tesla electric vehicles. The unit features an integrated battery management systems (BMS), liquid thermal management, and DC-AC inverter/charger. The new Powerwall 2 will have the capability to work in parallel with up to 9 units for homes/businesses with greater energy storage requirements.

COST: Approx $10,500 inc GST, excludes backup gateway

  • 13.5kWh usable for 3500 cycles - estimated 70% retained capacity

  • DC-AC Inverter included

  • Power output (AC) – Continuous = 5.0kW, Maximum Peak= 7.0kW

  • Round trip efficiency (claimed) = 89% including inverter losses

  • COST = $10,500** (US$8,500) – Cost per usable kWh = AU$768

  • Warranty is 10 years - See warranty certificate for more details.

    ** Approximate pricing July 2019, varies by state.

See the detailed Tesla Powerwall 2 review


DC Coupled Battery

Image credit: LG Chem

Image credit: LG Chem

LG Chem offer a large range of RESU (Residential Energy Storage Unit) batteries in various sizes from 3.3kWh up to 13kWh in two voltage options, 48V and 400V. Previously just the single 6.4kWh RESU6.4EX lithium battery was available.

The latest 48V range includes RESU3.3, RESU6.5 and RESU10 and just released RESU13 units with an option to combine different units using an adapter for up to 19.6kWh of total storage. More about the new range of new RESU batteries here.

LG chem use lithium polymer pouch with lithium nickel-manganese-cobalt (NMC) cell chemistry. The RESU batteries are housed in compact weather rated (IP55) enclosures with integrated BMS and are warranted to 10 years life, but this is to minimum 60% retained capacity (EOL). Based on current performance estimates it is expected the capacity after 10 years to be in the range of 70-80%.

COST - RESU H 9.8kWh - From $8800 inc GST

  • RESU10 - 8.8 kWh usable for 3500cycles to 60% retained capacity (EOL)

  • Power output – RESU10 48V = 5.0kW, Maximum Peak = 7.0kW

  • Round trip efficiency (claimed) = 96%

  • LG RESU10 = $7200** (US$5000) – Cost per usable kWh = AU$722

  • Warranty is 10 years - See warranty certificate for more details.

    ** Approximate pricing July 2019, varies by state.

See the detailed LG chem RESU review


DC Coupled Battery

Image credit: BYD

Image credit: BYD

BYD is the largest Chinese manufacturer of rechargeable lithium batteries and has dominated the Chinese electric vehicle and energy storage market for some time, however BYD is still relatively new to both Australia and north America. BYD manufacture a wide range of lithium energy storage systems for both commercial and residential applications using LFP or Lithium Ferro Phosphate cells which are considered the safest and most stable battery chemistry.

The BYD B-Box Pro range of low voltage (48V) batteries have become very popular due to the extremely competitive pricing and compatibility with many of the leading inverter brands. BYD also offer a range of HV or high voltage (400V) battery systems compatible with the emerging and popular hybrid solar all-in-one inverters for grid-connected homes.

The B-Pro Pro or Professional range of battery systems are made up of multiple 2.56kWh units and are available in a range of sizes from 2.5kWh (single unit) up to 10kWh with 4 battery units in a common steel enclosure. Additionally the largest B-box Pro module has 13.8kWh capacity (using two larger 6.9kWh units) and is fully scalable using up to 32 boxes in parallel.

The warranty is 10 years and specifies 60% EOL capacity or a minimum throughput energy as specified in the warranty document. The battery modules operate at the nominal voltage of 51V and have a high peak power output of 5.12kW over a short duration of 30 sec.

  • 2.56kWh (100%) usable for 10 years to 60% retained capacity (EOL)

  • Power output – Continuous @ 48V = 2.56kW, Max Peak 5.12kW (30 sec)

  • Power x 4 modules - Continuous = 10.24kW, Max Peak 20.48kW (30 sec)

  • Round trip efficiency = 95.3%

  • BYD B-Box Pro 10 (4 x 2.56kWh modules) = $7100** – Cost per usable kWh = AU$710

  • Warranty: 10 years to 60% retained capacity. Refer to warranty document here

    ** Approximate pricing July 2019, varies by state.

See the full BYD B-Box battery specification sheet here

SonnenBatterie ECO

AC Coupled Battery

Image credit: Sonnen

Image credit: Sonnen

Sonnen is the leading Germany lithium battery manufacturer and is the largest residential lithium battery system company in Europe. Until recently Sonnen had deployed the largest amount of home battery systems globally surpassing Tesla and LG. The SonnenBatterie ECO range is much like the Tesla Powerwall 2 in that it is an AC battery with built in DC-AC inverter but it still requires an additional solar inverter to function with a solar array.

There are two main differences between the Sonnen and Tesla AC batteries, the first being that Sonnen ECO is available in a range of different sizes with capacities from 3.3kWh up to 16kWh and the second is Sonnen use Lithium Ferro Phosphate or LFP battery chemistry as opposed to Lithium NMC of Tesla. Lithium LFP batteries are regarded as the safest and most stable battery chemistry with the longest life of up to 10,000 cycles.

Possibly the only real disadvantage of the SonnenBatterie ECO over other lithium battery systems is the limited inverter power rating which is a maximum of 3kW for single phase and 3.3kW for 3-phase systems.

See full SonnenBatterie ECO specification data sheet here

  • ECO10 - 10kWh usable for 3500cycles to 80% retained capacity (EOL)

  • Power output – Continuous = up to 3kW, Maximum Peak = 3.3kW

  • Round trip efficiency (estimated) = 92% including inverter losses

  • 10kWh ECO = AU$12,800** (US$9,500) – Cost per usable kWh = AU$1280

  • Warranty is 10 years - See warranty certificate for more details

    ** Approximate pricing July 2019, varies by state.

See the detailed Sonnen battery review

Battery comparison Results

Upfront Cost per kWh - usable capacity

Results include all eight batteries from the detailed solar battery review.

Battery upfront cost per kWh (usable capacity) - Including all battery systems in the solar battery review

Estimated battery life

Usable capacity remaining after 10 and 15 years **

Refer to the complete solar battery review for full details and comparison criteria.

AC Vs DC coupled Systems

An advanced AC coupled hybrid system using a DC coupled battery and multi-mode inverter.

For more details about AC vs DC coupled solar systems see our detailed comparison including the four main solar battery system types. It may sound confusing as DC batteries can be connected to inverters in either AC or DC coupled systems, depending on the installation type. Generally grid-connected homes use DC coupled systems while more advanced off-grid and larger scale systems are AC coupled systems, which are different to AC batteries.