General Motors CEO Mary Barra has announced what she described as a significant reduction in the cost of battery cells made at the Ultium Cells joint venture in Lordstown.

In an open letter to shareholders released as GM announced a 25% net income increase in the most recent quarter, Barra said the automaker is experiencing year-over-year improvements in profitability resulting from the benefits of scale, costs of materials, and other improvements.

As an example, Barra cited a lower cost of battery cells as the Ultium Cells plant in Lordstown ramped up production.

Barra also credited lower raw material prices as a factor in reducing costs.

The CEO said that lessons learned in Lordstown are helping ramp up production at the second Ultium Cells plant in Tennessee ramp up even faster.

According to the letter, battery module production has increased 300% over the last six months.

Predicting that Ultium will double its current battery module capacity by summer’s end, Barra described the quality of the modules as “very good and it’s continuing to improve.”

The letter goes on to say that Chevrolet, GMC, and Cadillac dealers in the U.S. translated rising Ultium Platform production into a 21% year-over-year increase in retail deliveries for electric vehicles.

“Improving module availability is enabling higher vehicle production, which we believe will help us win even more new customers in the growing U.S. EV market,” according to Barra.