By Nick Carey

LONDON (Reuters) -Slovak startup InoBat plans to launch a battery designed for military drones and unmanned aerial systems, it said on Monday, as it responds to an upsurge in European defence spending.

The company will start producing the E10 cell in September and is in "in early-stage collaboration with selected European drone manufacturers," CEO Marian Bocek told Reuters.

"We are engaging with drone manufacturers that require a technologically superior European battery solution," Bocek said.

The company's previous focus has been electric vehicle and electric vertical take-off and landing vehicle batteries.

As Europe scrambles to increase production of tanks, radars and weapons following U.S. President Donald Trump's demands that it take care of its own defence, some companies have begun retooling automotive plants for military production.

Rheinmetall, Europe's largest ammunition maker, for instance, has said it will repurpose two automotive parts plants to make defence equipment and French munitions company Europlasma is taking over a foundry formerly owned by French carmaker.

InoBat said the E10 cell charges in under 15 minutes, can handle a 40% greater payload and provide 60% longer flight time than cells currently on the market.

Bocek said it was "was a natural evolution" for InoBat "driven by demand for European-made, high-spec batteries in both defence and industrial drone markets".

The Slovak battery maker has raised over 400 million euros ($447 million), including 100 million euro in funding announced in December.

Chinese battery maker Gotion holds a 10% stake in InoBat, and the two companies have a joint venture that will start producing EV batteries for Volkswagen in 2027.

CEO Bocek told Reuters the drone battery business is separate from its joint venture with Gotion and is entirely compliant with NATO supply chain requirements.

($1 = 0.8942 euros)

(Reporting By Nick Carey; editing by Barbara Lewis)