Hi Ryan, with out more information about your laptop, would suggest that you click on item to go to the page that lists all the details about this item.........such as; is your laptop made by HP? If so.....then is your model listed? If your laptop is made by another company...try searching Amazon for that company's products. Happy Shopping Blessings!
Sorry, i bought this item for a friend's computer...don't remember what kind she has. http://www.amazon.com/genuine-Original-battery-4331S-laptop/dp/B00DH6CUFC check this page on Amazon for the correct one for your Probook 4540.
if link does not work, search amazon for: probook4540 battery charger. Hope this helps. Blessings!