The potential costs to Greatbatch Inc. keep mounting from the verdict earlier this month in a competitor’s lawsuit against the Clarence medical device and battery maker.

A Louisiana state court judge this week upheld a jury’s $21.7 million verdict against Greatbatch in a lawsuit filed by Ion Geophysical Corp. alleging that Greatbatch fraudulently used Ion’s product designs to develop its own competing product.

The judge also expanded the size of the verdict by allowing Ion to collect its attorney’s fees and costs, as well as interest that has accrued on the verdict from the time the lawsuit was filed in 2002. That would add nearly $11 million to the verdict, bringing it to a total of $32.7 million.

That sum could continue to rise because the judgment, if upheld on appeal, will accrue interest at an 8.5 percent annual rate until it is paid, Ion said Friday in a filing with the Securities and Exchange Commission.

Greatbatch is appealing the jury verdict, which company executives said is disproportionately large, given that the company has earned less than $1 million in profits over the last eight years from the battery covered by the lawsuit.

The lawsuit stems from a failed business transaction dating back to 1997. Ion alleged that Greatbatch used its product designs and other trade secrets on a type of battery that its Electrochem commercial battery subsidiary makes for the geophysical surveying and seismic markets. Greatbatch executives contend that the verdict “is unsupported by the facts and the law.”

Greatbatch initially won a summary judgment to dismiss the case in 2007, but Ion appealed, and the Louisiana Court of Appeals reinstated the case in January 2008.