German storage system manufacturer Sonnen has published test results that indicate the longevity of its products after extended use. In laboratory tests, the lithium iron phosphate (LFP) battery cells, which are also used in the company's “solar battery,” reportedly withstood 28,000 charging cycles.

The lifespans of battery storage systems remain an issue for many potential buyers. Sonnen says that it has charged and discharged battery cells at a C rate of one and a depth of discharge of 100% over a period of eight years. This means that a full charge or discharge was completed within an hour. It noted that the test for the batteries was significantly more demanding than its use as a residential storage system.

Over the past few years, it has carried out tests in a laboratory operated by Sonnen in Wildpoldsried, Germany. According to the manufacturer, the iron phosphate battery cells still had 65% of their original capacity. As a result, the cells have not yet reached the end of their lifespans, because for this there must be a sudden drop in capacity, the manufacturer explained.