Two will be acquired by Caterpillar subsidiary Progress Rail, while the other two are being supplied by Wabtec.
All four are expected to be delivered in late 2023.
BHP will test the battery electric locomotives' performance and emissions reduction capabilities in delivering iron ore from its Pilbara mines to the Port Hedland export facility.
The company said conducting the trials in collaboration with two leading providers would support its planned electrification of its iron ore fleet of more than 180 locomotives.
BHP expects a full transition to battery electric locomotives would reduce BHP's WA iron ore diesel-related carbon emissions by roughly 30% annually.
"WA Iron Ore is significant within BHP's global operations, and I am pleased we can play a leading role in helping to develop new and innovative solutions with potential to shape our business for a cleaner future," BHP WAIO asset president Brandon Craig said.
"Rail is the fundamental link in our pit-to-port value chain, and the power required to deliver fully-laden iron ore wagons from the Pilbara to Port Hedland is significant.
"Trialling battery electric locomotives in collaboration with Progress Rail and Wabtec has great potential to support our operational emissions reductions targets and goals."
The trials will also test unique ‘energy recapture' opportunities using the rail network's natural topography to further reduce the trains' overall power demand.
On the way to port, locomotives can capture energy from braking on downhill slopes (energy that would otherwise be lost) and use it to help power empty trains back to the Pilbara.
A fully-laden BHP WA Iron Ore train typically comprises four diesel-electric locomotives pulling approximately 270 cars carrying a total of 38,000 tons of iron ore.
"Replacing diesel-powered vehicles with electric technology is a key part of our plans to reduce operational emissions, as is partnering with a broad range of global equipment manufacturers and technology providers," BHP group procurement officer James Agar said.
"By working with two global leaders in Progress Rail and Wabtec, we can broaden the scope of our trials and be better informed as we prepare for the planned replacement of our diesel-powered iron ore rail fleet. This is a good first step with significant potential."
All three Pilbara iron ore majors have announced battery locomotive trials since the start of the year.
Fortescue Metals Group agreed to acquire two locomotives from Progress Rail, while Rio Tinto will take delivery of four Wabtec locomotives next year.
