The companies said no details, including the investment amount, timing and ownership of the potential venture, had been decided.
Nissan, Japan's second-biggest auto maker, last week had unveiled plans to develop a new lithium-ion battery to be manufactured and sold through a separate company as part of its efforts to offer less polluting vehicles. It gave no details on the company at the time.
Business daily Nihon Keizai reported on Thursday that Nissan and NEC would set up a joint company next year, aiming to begin mass production of the batteries by 2010.
"It's true that we are considering a tie-up, but no decision has been made on the numbers," said NEC spokesman Hideyuki Nakajima.
A Nissan spokeswoman echoed his comment, but added that the batteries would have to be ready for the auto maker's planned launch of its first gasoline-electric hybrid car developed in-house in the 2010/11 business year.
Nissan is also planning to start selling pure electric vehicles using the new batteries in the early part of the next decade.
The Nihon Keizai said Nissan, which trails Toyota Motor Corp. in the development of fuel-efficient vehicles, is likely to take less than a 50 percent stake in the joint venture.
A decision on the tie-up will likely come in the new year, sources familiar with the matter told Reuters.
NEC estimates the lithium-ion battery market for hybrid cars would grow to 300 billion yen ($2.5 billion) in 2015.
NEC had previously partnered Fuji Heavy Industries Ltd. to develop lithium-ion batteries for cars but they dissolved the partnership early this year when the maker of Subaru cars formed a capital alliance with Toyota.