Redflow is selling batteries again. After informing investors about a range of technical issues with its residential flow battery in late April -- including electrolyte impurities that could cause system failure -- the Australian startup is delivering units to customers.

CEO Simon Hackett sent a letter to investors today informing them that testing was successful. "A first round of laboratory test that 25 batteries in stock meet Redflow quality standards, enabling their immediate delivery to customers."

Redflow makes a miniaturized zinc-bromide flow battery for residential applications, called the ZCell. The company claims it outperforms lithium-ion batteries in nearly every way, including per-kilowatt-hour cost. One comparison from SolarQuotes put the levelized cost of energy of the ZCell below many competing lithium-ion products.

But Redflow faced technical challenges early. In a letter penned to investors last month, Hackett explained that 23 batteries were repaired or replaced in the first few months of 2017. In addition, the company uncovered electrolyte impurities that threatened another 10 batteries. Redflow sent 20 batteries to a lab for testing and reassessed its supply chain. 

"The very latest thing reported in that document is a straight supply chain issue -- one of the components that goes into the battery has had an issue with a contaminant that we’ve found in one batch of raw materials. So we’re dealing with it, and we think we’re on a good path to sorting it out soon," wrote Hackett in an email to GTM in April. 

"I’m not really in a position to elaborate further on the technical detail beyond the above, as it starts to enter into the realm of aspects of our technology that are protected as industrial trade secrets," he wrote.

Hackett didn't provide much detail on the latest development either, except to say that test results of a "product remediation process" were positive. 

"This process will be applied routinely to any battery subsequently identified as requiring it, to ensure that all batteries shipped to customers meet appropriate quality standards," wrote Hackett.

The company says it has USD $740,000 in backorders so far, with 96 residential batteries ready for sale and 120 batteries fully completed at the production facility.

Redflow also announced its first contract in the telecom market. In February, the startup's global sales director said Redflow was eyeing remote infrastructure in the Asia-Pacific region.

Hitech Solutions, a New Zealand-based telecom infrastructure company, is buying USD $600,000 worth of batteries for remote island applications. Details were sparse, but Hackett said the deal "supports the first stage of a multiple-stage project."

Further reading about Redflow:

Redflow Halts Delivery of Residential Flow Batteries Due to ‘Unexpected Product Failure Modes’

Can Flow Batteries Beat Lead-Acid in Asia’s Telecom Market? Redflow Thinks So

Why the Australian Solar-Plus-Storage Market Looks So Bright