Wesfarmers has sparked concerns among some investors about cost blowouts associated with its push into battery metals mining and processing after taking a big step forward in its $776 million takeover of lithium play Kidman Resources.

The Rob Scott-led Wesfarmers is on track to complete the takeover by September but on completing due diligence it has added $100 million to the capital costs it will cover for the development of the Mount Holland lithium mine in Western Australia and a lithium hydroxide plant.