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Which solar battery is the best?

Image of all batteries compared in this document

Comparison of batteries currently available in the UK

Energy Storage Systems (ESS) have fallen significantly in cost, and can greatly increase your self-consumption of solar PV energy. Rising electricity prices have meant solar batteries for domestic households have become more and more popular – but which battery is the best right now?

Unfortunately, the question of which battery is best is not necessarily that simple. While the Tesla Powerwall 2 may offer good value storage capacity – in order for an ESS to be cost-effective, it is imperative that you select the battery which best matches your individual system and requirements.

Below, we have outlined the specifications, and what we regard as the positives and negatives of a few of the most accomplished domestic battery systems currently available in the UK.


An important factor to consider is the size of the battery you choose. Too large a capacity, you might install more storage than you can fill. Too small, you might end up needing to install further capacity (at a higher price than installing a larger battery initially).

It’s not just size that matters either. With an abundance of new battery manufacturers presenting new products to the market, making sure you get a competitive cost, as well as a reliable and comprehensive warranty are both important elements to consider.

Tesla Powerwall 2

Marketing photo of Tesla Powerwall 2

The Tesla Powerwall 2 is far and away the most publicised battery out there, and it’s also currently the best value. The 13.5kWh unit costs roughly £7500 plus VAT – including installation, and the known branding and style makes it an appealing and sought-after system.


  • The Powerwall 2 has a much larger capacity than its other main competitors.
  • It is AC coupled, which means you won’t have to install a separate (and potentially expensive) charge controller.
  • Strong 10-year performance warranty from a reliable brand, ensuring 80% retention after 10 years.
  • It can be installed both inside and outside, and mounted on the wall or floor.
  • User friendly app allows you to monitor the Powerwall 2, along with your solar PV, or Tesla Vehicle.
  • A Tesla Powerwall system is easily scalable, and capacity can be increased to 10 Powerwall 2’s in one system.
  • Access to prefential electricity tariffs such as the Octopus / Tesla plan which could allow you to benefit from flat import/ export rates as low as 8p/kWh for qualifying customers.


From the negative perspective, the large capacity of the Powerwall 2 means the battery may not charge fully from the solar PV on low output days. For those with smaller PV systems or minimal excess generation, be wary of paying for more storage than is required.

Technical Specs

Usable Capacity: 13.2kWh

Lifetime charge cycles:  Unlimited

Efficiency: 89% round-trip efficiency

Max continuous power: 5kW

Operating Temperature: -20°C to 50°C

Dimensions: L x W x D: 115cm x 75.5cm x 15.5cm

Weight: 122 kg

Performance Warranty

The Tesla Powerwall 2’s Performance Warranty for self-consumption and backup use ensures performance of no lower than 80% energy retention after 10 years, following initial installation, with unlimited charge cycles if connected to solar. For any use other than self-consumption/backup, the Performance Warranty ensures 80% energy retention after 10 years following initial installation date – with 37.8MWh of aggregate throughput.


Marketing image of the sonnenBatterie

Sonnen’s energy storage system (ESS), the sonnenBatterie, has a good track record in Germany, where the ‘Sonnen Community’ scheme allows a network of batteries to interact and trade power between each other. It comes in 2kWh ‘blocks,’ starting at £3800 each plus VAT – fitted.


  • The sonnenBatterie has an easily expandable capacity, and is scalable up to 16kWh, or 8 batteries in total.
  • Like the Tesla, it is AC coupled with an inbuilt charge controller.
  • The sonnenBatterie is a small and stylish unit.
  • With the ‘sonnenApp’, you’ll be able to check your energy usage and production to monitor, analyse and control the supply and demand of your household.


  • Very high £/kWh. If you require larger capacity, scaling up in 2kWh blocks will prove more expensive than opting for a larger battery system in the first place.
  • It can only be mounted indoors.

Technical Specs

Usable Capacity: 2kWh

Lifetime charge cycles:  10,000

Efficiency: 98% maximum efficiency

Max continuous power: 1.5kW

Operating Temperature: 5°C to 40°C ambient

temperature range

Dimensions: height x width x depth: 70  x 64 x 22


Weight: 55 kg

Performance Warranty

Storage capacity will be not less than 70% of the labelled storing capacity over the duration of the warranty period. The warranty period for the Performance Warranty terminates upon the earlier of (i) 123 months after purchase of the Covered Product, or (ii) 120 months after installation of the Covered Product by an Authorized Dealer, or (iii) 10,000 full (100%) charging cycles of the Battery Pack.


LG Chem RESU marketing photo

The LG Chem RESU is a good quality product from a proven manufacturer. As it is DC coupled, the system will require integrating with a Power Control System for to work alongside solar PV systems. With the market leading 13.5kWh Tesla Powerwall battery, and multiple smaller capacity storage systems, the 6.5kWh LG Chem RESU offers the clearest appeal out of its 3 available sizes. The 6.5kWh unit is available from £4500 plus VAT – fitted, dependant upon the charge control system.


  • Advertised 80% capacity retention after 10 years.
  • It is available in a variety of sizes (3.3kWh, 6.5kWh, 10kWh), with the 6.5kWh unit offering a good value mid-range choice.
  • It can be mounted inside or outside.
  • Using a RESU Plus (expansion kit) up to 3 batteries can be cross-connected to increase the usable capacity (however, if you plan to expand your capacity, a 13.5kWh Tesla Powerwall 2 may be a better selection).


  • Installing a separate charge controller complicates the installation procedure, increasing both component and installation costs.
  • It isn’t the most aesthetically pleasing design compared with some of its competitors.
  • Warranty covers for 60% retention after 10 years, 10-20% less than competitors.

Performance Warranty

The Performance Warranty for the LG Chem RESU is valid for 10 years from the initial installation date and warrants and represents that the Product retains at least 60% of Nominal Energy for either 10 years after the date of the initial installation or for a minimum Energy Throughput of 16.1MWh

Technical Specs

Usable Capacity: 5.9kWh

Lifetime charge cycles:  6,000

Efficiency: 95% round-trip efficiency

Max continuous power: 4.2kW

Operating Temperature: -10°C to 45°C

ambient operating temperature

Dimensions: width x height x depth: 45.2 x 65.4 x

12 (cm)

Weight: 52 kg


Photo of wall mounted BYD B-Box Battery

BYD are a long standing and reliable Chinese manufacturer of electric vehicles and rechargeable batteries. Their 2.5kWh B-Box ESS is available from £1800 plus VAT fitted, and will require integrating with a separate charge control unit for retrofit to existing solar PV systems. The system can be wall mounted, or scaled by adding up to 3 additional 2.5kWh battery storage units to a B-Box battery cabinet. Up to eight 10kWh battery cabinets can be combined in parallel to create 80kWh of storage.


  • BYD provide a strong warranty, ensuring 80% capacity retention after 10 years (for 1 cycle per day).
  • The B-Box currently provides the best value for small storage capacity, which may prove more cost-effective than larger batteries like the Tesla if better matched to your consumption, despite a higher £/kWh.
  • Easily scalable in 2.5kWh units.


  • Can only be mounted indoors.
  • Not very stylish or aesthetic, for a more visually pleasing system you may rather pay extra for a sonnenBatterie or Enphase storage system.
  • The requirement for a separate charge controller when using in tandem with PV means a more complex installation.

Performance Warranty

10 years warranty for > 80 % usable capacity at a maximum of one full cycle per day.

Technical Specs

Usable Capacity: 2.4kWh

Lifetime charge cycles:  >6,000

Efficiency: >97%

Max continuous power: 2.56kW

Operating Temperature: -0°C – 55°C

Dimensions (of box): width x height x depth:

60 x 88.3 x 51 (cm)

Weight: 88kg

Enphase AC Battery

Enphase AC Battery marketing photo


  • The Enphase battery has an easily expandable capacity and simple installation process.
  • It is a small and compact unit which looks simplistic and stylish.
  • It is AC coupled and doesn’t require an integrated charge control system
  • It has some neat software which is user friendly and accessible via their app.


The main drawback of the Enphase AC Battery is it has a high price per kWh of storage when compared with its competitors.

Performance Warranty

If average annual internal AC Battery temperature is below 28°C
Year 1 or 0.74 MWh AC energy throughput Cumulative average capacity at least 90%
Years 2-5 or 3.53 MWH AC energy throughput Cumulative average capacity at least 85%
Years 6-10 or 6.65MWh AC energy throughput Cumulative average capacity at least 70%
If average annual internal AC Battery temperature is between 28°C and 37°C
Year 1 or 0.72 MWh AC energy throughput Cumulative average capacity at least 88%
Years 2-5 or 3.32 MWH AC energy throughput Cumulative average capacity at least 80%
Years 6-10 or 5.82 MWh AC energy throughput Cumulative average capacity at least 70%

Technical Specs

Usable Capacity: 1.2kWh

Lifetime charge cycles:  >7300

Efficiency: 96% round-trip efficiency

Max continuous power: 0.26kW

Operating Temperature: -20°C to 45°C (ambient

operating temperature)

Dimensions (of box): width x height x depth: 39 x

32.5 x 22 (cm)

Weight: 25kg

Table comparing specifications of all battery systems featured in this article