ETA-Leveling enables second-life battery applications with “pick-n-mix” cells connected in series

Operating battery cells connected in series – from different manufacturers, of different ages, and at different nominal capacity: ETA-Leveling makes it possible. It is the only charging process available enabling the simple reuse and repurposing of, for example, cells from power storage modules declared defective.

It goes without saying that completely randomly combined cells do not represent a useful second-life application. However, it has been demonstrated that such cells can be connected and operated in series and leveled using the straightforward ETA-Leveling process. This has been labelled disruptive – justifiably so – and can be completed in as little as a few hours. The resulting “patchwork battery” can be operated long-term without any issues. During charging, each cell is treated as if it was part of a single-cell battery application – thanks to efficiency leveling. This disproves the long-held assumption that the cells within a battery block need to be as identical as possible, and that even minor differences complicate or impede operation.

No more recycling unless a battery is actually defective

In light of large numbers of discarded battery modules piling up in manufacturer’s storage facilities and many more returning items that will join them in the years to come, this can be considered a revolutionary technology. Depending on a module’s designated application, it can retain as much as 80 % of its original capacity. Its current capacity results from individual, prematurely aged cells that unbalance the block and by doing so cause the actual defect. This means that the weakest cell within a module determines the entire block’s capacity. In turn, this translates to most of the cells within discarded battery blocks still being in excellent condition – or at least too good to recycle them. ETA-Leveling makes it possible to connect and operate very different cells in series: the first-of-its-kind, easy solution to continue to use these cells. “Up until recently, we ourselves would’ve never thought that combining cells randomly would work. It has not been possible with any of the traditional BMS,” says Frederik Fuchs, Managing Director of Benning CMS Technology. “Manufacturer, age, nominal capacity, cell chemistry – it really doesn’t matter. Our leveling process also recognises which cells are a reasonably sensible match based on their capacities. We then combine these cells to a long-lasting battery block that works perfectly.” This unlocks unprecedented opportunities for reusing discarded battery modules. Whether the aim is repurposing or processing to varying degrees (refurbishment, reconditioning, remanufacturing) – all possible scenarios become significantly more simple.

Licences for ETA-Leveling, which is suitable for battery blocks of all kinds and requires no hardware changes, recently became available for purchase.

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Eine mit ETA-Leveling betriebene Patchwork-Batterie: Alle Zellen sind gebraucht, teils haben sie mehrere Jahre gestanden, die größte Zelle verfügt über 68,6 Ah, die kleinste über 45,9 Ah
A “patchwork battery” operated using ETA-Leveling: All cells are used and some have been stored for several years; the largest cell has a capacity of 68.6 Ah, the smallest of 45.9 Ah.
A “patchwork battery” operated using ETA-Leveling: 33 % capacity difference between the largest (68.6 Ah) und the smallest (45.9 Ah) cell 
Die Patchwork-Batterie wird mit 80 % DoD (Depth of Discharge) von 45,9 Ah (kleinste Zelle) betrieben. Sie kommt somit auf 36,72 Ah nutzbare Energie im Regelbetrieb.
The “patchwork battery” is operated at 80% DoD (depth of discharge) of 45.9 Ah (smallest cell). This results in 36.72 Ah of usable energy (standard operation).

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Leveling rather than balancing…
…because it does away with the battery resting periods

Battery resting periods are used for balancing in electromobility. However, balancing can only start once the charging process is finished, which causes considerable delay. The batteries of electric cars that are driven every day may never have a true resting period. This is where battery management systems (BMS) are advantageous, because instead of balancing based on voltage, they level, i.e. carry out efficiency leveling. Leveling only takes a few seconds without the need for resting periods. 

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