HEIWIT sodium battery: 9,000 cycles at 95 per cent depth of discharge (DoD) % for energy storage

Updated on 17 September 2026

Over the last few months, we’ve been telling you how the world of energy storage is changing: the limitations of traditional chemical technologies, the race for critical materials, and the search for safer and more durable solutions. Our last article ended with a question: “What if someone had already done it?”. Today we can provide an answer. HEIWIT has developed, tested and validated a new HEIWIT sodium battery based on sodium-ion cells with polyanionic chemistry, designed with a specific goal in mind.

Not just a battery designed to store energy, but to do so every day, thousands of times, safely.

What we announced: the HEIWIT sodium battery

Development has been completed and validation has been finalised. These cells will go on sale from November 2026: The Heiwit systems currently available on the market are fitted with layered oxide cells, with a stated cycle life of 6,500 cycles. If you’re considering a purchase right now, this is the figure that matters to you. We’re talking about a storage system that isn’t based on lithium, but on sodium – an element that is far more abundant and widely distributed. The polyanionic chemistry is what makes this battery particularly stable and suitable for intensive, repeated use over time.

The figure that sums it all up is the expected cycle life: 9,000 cycles at DoD 95%. To understand what this means, think of a household battery that charges and discharges once a day: 9,000 cycles are equivalent to around 24 years arithmetic one cycle per day. This is a rough estimate, not a calendar-based life expectancy: the actual lifespan depends on temperature, average state of charge and actual depth of discharge.

The key features that really matter

We have focused on the factors that make a difference to those who install, design and manage systems:

• Extended service life: 9,000 cycles at a DoD of 95%, designed for intensive use and frequent, deep discharges.
• Absence of lithium, cobalt and critical materials: less reliance on fragile supply chains and contested raw materials.
• High thermal and chemical resistance: polyionic sodium-based chemistry is inherently more stable, which is a tangible advantage in both domestic and industrial settings.
• High-current resistance: stability during charging and discharging, even at high power levels (sustained C-rates).
• Good performance at low temperatures: more consistent performance, even when the cold causes problems for other chemical products.
• Lowest lifetime cost of stored energy: more productive cycles mean a lower cost per cycle.

There is just one common thread: a battery that can handle daily, prolonged use.

What difference does a heavy-duty battery actually make?

The right question is not “how much energy does it contain?”, but “how many times can it release that energy over time, safely and without degrading too much?”. This is where a battery designed for longevity changes the game.

Let’s take a practical example. A system that cycles many times a day — for energy arbitrage, for grid services or for an activity with intermittent consumption — puts any storage system under strain. With a high cycle life, this intense workload does not result in early replacement: the battery continues to do its job, day after day, with slower degradation.

Sodium vs lithium batteries: a comparison based on real-world performance metrics

We want to be honest about the figures, as always. We’re not saying that “lithium is outdated”: where it’s needed, the maximum energy density When it comes to compact size and low weight, lithium remains a competitive choice. The comparison only makes sense when based on concrete parameters and in the right scenarios.

The HEIWIT sodium battery really shows its advantages when it counts:

• Cycle life: more cycles available over the service life.
• Security: greater thermal and chemical stability.
• C-rate and intensive use: resistance to high currents and frequent cycling.
• Low temperature: more consistent performance in cold conditions.
• TCO and cost per cycle: the lowest total cost of ownership in high-usage scenarios.

Every comparative statement is based on tests carried out under the same operating conditions.

Where it is used: residential, industrial and BESS

The very concept of accumulation manifests itself in three ways:

• Residential storage: for those seeking self-consumption and self-sufficiency with a safe and long-lasting system, also suitable for intensive daily use.
• Industrial accumulation: for businesses with high and irregular consumption, where durability and safety translate into operational continuity.
• BESS (Battery Energy Storage System): for network-scale applications, where the number of cycles and the cost per cycle determine the project’s economic viability.

The validation process

An announcement like this does not come out of the blue. The product has undergone a development and validation process that includes cycle testing, safety tests and the collection of long-term degradation curves. The aim is to demonstrate, with verifiable data, that the product’s performance claims hold true under real-world working conditions.

International research into sodium-based chemistry confirms the potential of this line of enquiry. You can find out more about the scientific aspects by consulting the studies published on ScienceDirect: first article e second article.

A different way of thinking about accumulation

The HEIWIT sodium battery stems from a simple yet demanding idea: to design a storage system not for a single peak demand, but for day-to-day, repeated and reliable operation throughout the plant’s entire lifespan. It is a shift in perspective that appeals particularly to those who think in the long term and consider the true cost of stored energy.

Would you like to find out more? Here’s how

If you are an installer, a designer, an energy manager or a BESS operator, now is the right time to get in touch with us. You can:

• Request information on the new HEIWIT sodium battery.
• Receive the technical documentation along with the official product specifications.
• Apply for the first BESS pilot projects and initial installations.
• Discover the apps for residential, industrial and grid-scale storage.

Contact the HEIWIT team: let’s work together to build a storage system designed to operate safely every day, thousands of times over.

The announcement of the HEIWIT sodium battery has now resulted in a product being added to the catalogue: the HEIWIT-NA, 10 kWh with a downloadable datasheet, whilst an overview of the technology can be found in the sodium range page.