Shares of Johnson Controls were up 3.5 percent at $35.40 before the bell.
The deal will allow Johnson Controls to focus on its building technologies and solutions business, which makes heating, ventilation and air conditioning systems, as well as building access control and fire detection systems.
Reuters had reported, late last month, that Brookfield and Johnson Controls were close to finalizing terms for the sale of the unit, whose batteries are used in about a third of cars globally.
The deal represents the biggest shake-up at Johnson Controls since its merger in 2016 with Tyco International.
Johnson Controls' power solutions business, which makes and distributes about 154 million lead-acid batteries for passenger cars and light trucks annually, carries higher margins but has been capital intensive for Johnson Controls, analysts have said.
The company expects to deploy $3.0 to $3.5 billion of proceeds toward debt paydown and retain an investment grade credit rating, the company said in a statement.
More deals in the sector are likely, as industrial conglomerates continue to separate businesses that are too disparate in terms of financial performance.
The company expects the transaction to close by June 30, 2019.
Centerview Partners and Barclays were financial advisers to Johnson Controls, and Simpson Thacher served as legal advisers.
(Reporting by Sanjana Shivdas and Rachit Vats in Bengaluru; Editing by Shailesh Kuber)
By Sanjana Shivdas