energy news

Battery storage: breaking down a datasheet

Using the sonnen UK datasheet, we explain what all the specifications on a battery’s datasheet mean.

It’s important for you to have a basic understanding of what your battery is made of and what it can do. Especially, if you are considering buying a battery to retrofit to your existing solar PV system.

Sonnen is a German company and is an industry leader of many international home battery storage markets. The sonnenBatterie is a smart storage system that automatically adjusts itself to help optimize your energy consumption and the combination of a sonnenBatterie and a solar PV system will give you access to your clean self-generated energy whenever you need it. We’ll be breaking down their UK datasheet on the battery designed for single-phase supplies.

city with lights on

Nominal battery capacity in kWh

This is how much electricity each of the units can store. The units’ capacities range between 5.0-15.0 kWh.

Usually, capacity is measured in amp-hours (Ah) but Sonnen has translated this into kWh to make it more accessible to the reader. To do this, they would have multiplied the Ah by voltage (V).

The capacity is labelled as nominal but on other data sheets, “rated” is sometimes used instead.
“Nominal” means in name only. So, Sonnen is stating this either to say that capacity can be achieved under certain conditions (e.g. the discharge current and operating temperature) or in relation to the Depth of Discharge (DoD) which is specified below.

Depth of Discharge (DoD)

The depth of discharge is measured in a percentage (%). A battery will go through cycles, which is a full charge and discharge. However, a battery won’t charge and discharge at its nominal capacity. It will only use the percentage of the battery’s capacity.

Sonnen’s depth of discharge is measured at 90%. This means if you had a 15 kWh battery, you would be able to charge the capacity up to 13.5 kWh. This is sometimes referred to as the “usable capacity”.

The depth of discharge is to prevent a deep discharge or overcharge. A battery needs to retain some charge to prolong its lifespan. The battery’s automated management system will do this.

90% is a really high depth of discharge. Many lithium batteries are only at 70-80% whilst other chemical types, such as lead-acid, can even be below 50%.

Cell technology

There is a range of different battery chemical compositions. Sonnen, like most grid-tied home storage, is lithium iron phosphate. There are other battery types available like lead-acid but lithium will likely be the main battery type we use for the next decade.

As there is a range of capacities available, the units come in different shapes and sizes. Sonnen’s battery has the added benefit of being scalable; if you wanted to increase the capacity of your battery, you could by adding more cabinet options rather than having to purchase another standalone battery.

The weight is measured in kilograms (kg) and the dimensions are for the height, width and depth (H/W/D) and are measured in centimetres (cm).

The battery can be installed standing on the floor or mounted on a wall. The battery isn’t weatherproof so it needs to be installed internally. However, you can purchase an external enclosure for the unit so it’s safe to be installed outside.

Nominal power (charging/discharging) in kW

This is the input/output of the battery at any given time. If the Sonnen battery has a capacity of 5 kW, the charge/discharge is at 2.5 kW. At a capacity of 7.5-15 kW, the charge/discharge is at 3.3 kW at any given time.

The conditions which would affect the nominal power is the C-rate of the battery, temperature, etc.

Max. inverter efficiency

A solar battery will have an internal/external inverter to convert the electricity from AC to DC or DC to AC to ensure the electricity is stored safely.
The maximum inverter efficiency is measured in a percentage (%). Most battery models and inverters, in general, will have efficiencies of +90%. This means that the battery can charge or discharge at a maximum of 95% of its nominal power.

However, this percentage needs to be accounted for twice in order to calculate the correct round-trip efficiency. As the electricity will be charged to be stored in the battery and then convert again to be discharged.

The efficiency would be affected by the same conditions as the nominal battery capacity and power. The main factor would be the temperature as if an inverter gets too hot, it will become less efficient and if a battery gets too cold, it will get less efficient too.

Max. battery efficiency

This is the same as above. It is natural that the efficiency of a unit will be under 100% and will have a certain amount of losses. The maximum battery efficiency is also measured as a percentage (%). This efficiency is rated at 98%.
So, without accounting for the PV inverter’s efficiency, you would need to account the efficiency of the electricity when charging the battery, when storing in the battery and when discharging from the battery.

Example: A 5 kW Sonnen battery has a nominal power of 2.5 kW. The loss in efficiency would be 2.5 x 0.95 x 0.98 x 0.95 = 2.211125 kW.

Ambient temperature range

Usually, ambient temperature is used in a computing context. It is the air temperature that will be of the environment the battery is installed in. Sonnen has labelled that the battery operates sufficiently between the temperatures of -5°C – +45°C.

Dust and water protection

The battery has an IP rating of 30. The IP code is an International Protection rating marking that classifies and rates the degrees of protection provided against intrusion, dust, accidental contact, and water in mechanical casings and electrical enclosures.

Operating mode

As mentioned, this particular datasheet is for a single-phase battery. This just means the unit is designed for use on properties with a single-phase supply. Most homes and other domestic properties have this type of supply.

Larger businesses, farms and commercial properties will likely have a dual-phase or three-phase supply.

Tests and directives

The test and directives are to show that the battery has both been manufactured and supplied within regulations.

Battery service life

Sonnen is stating here that the battery is designed to operate sufficiently for 20 years. This is a figure to consider when calculating your return on investment.


The unit is actually warranted for 10 years. In the small print of the datasheet, Sonnen states this is for “all parts”.


The number of cycles is in direct relation to the warranty. Sonnen advertises that the battery is warranted for either 10 years or 10,000 cycles, whichever comes first.
As mentioned before, a cycle is a full charge and discharge.

That’s the Sonnen single-phase battery datasheet broken down. The battery also has the capability of charging from the grid as well as operating during a power outage.

As well as using more of your free solar energy, you can also benefit by charging from the grid. If you switch to a time-of-use tariff through your energy supplier, you can store cheap electricity at off-peak times and then use this or your free electricity during on-peak times.

We also offer a range of different manufactured batteries too. Some of the brands include BYD and Solax. You can enquire with us for transparent, unbiased advice on if battery storage will work for you or not, anytime.

You can speak to us via web chat or phone in at 0800 856 2200. We also have web forms on our website for you to put your details in. Our general email address is

Get in touch

Follow us:

Call us:

0800 856 2200

Email us:

You may also be interested in:

Solar panels for our family home

Solar PV and battery storage customer, Jeffrey, has saved over a tonne of CO2 in just 6 months! Read the blog.

Case Study: Solar Panels and sonnenBatterie

Solar PV and battery storage customer, Jeffrey, has saved over a tonne of CO2 in just 6 months! Read the blog.

Solar energy shunned in UK party election

Which, if any, party acknowledges the great importance of solar energy to tackle climate change? Read the blog to find out!

The 6 easy steps of solar PV and battery storage

How solar worksThe 6 easy steps of solar PV and battery storageSolar PV is a well established...

Floods, fires and failing politicians

Extreme weather is currently wrecking millions of lives across the globe. So, what role does climate change have to play in these disasters?

About Solar Plants

Refer a friend


About Solar Plants

Refer a friend


Contact us

Get in touch

Chat with us

Contact page

6 + 5 =


Case studies



Case studies