BRUSSELS (Reuters) - A group of car starter battery makers will contest European Union accusations of operating a cartel to fix battery prices at a closed hearing next week, people with direct knowledge of the matter said on Wednesday.

The companies are Banner, Clarios, Exide, FIAMM Energy Technology (FET) and its predecessor Elettra, and Rombat

Together with trade body Eurobat and its service provider Kellen, which were also charged by the European Commission, the companies will present their arguments at a week-long hearing in Brussels, they said.

Companies usually plead their case at such events before senior Commission officials and their peers from national competition agencies, rivals and customers. That could lead to regulators narrowing their charges, although this is rare.

The EU executive, which also acts as the EU competition watchdog, accused the group last year of colluding to increase the prices of automotive starter batteries sold to car producers in Europe.

It said this took place between 2004 and 2017, during which the seven participants created, published and agreed to use new indexes in their price negotiations with carmakers in the so-called Eurobat Premium system.

The Commission, Banner and FET declined to comment. Clarios, Exide, Rombat, Eurobat and Kellen did not immediately respond to requests for comment.

The companies, which make 12-volt lead batteries used to start most combustion engine cars, risk fines as much as 10% of their global turnover if found guilty of breaching EU antitrust rules.