John Mayer's new single 'Half of My Heart' has the alternative rocker crooning about having to let go of a relationship for not loving whole-heartingly: "Your faith is strong / But I can only fall short for so long / Time will hold, later on / You will hate that I never gave more to you than half of my heart." Featuring echoed and subtle harmonized vocals by Taylor Swift, the track swoons us with Mayer's melancholy electronic guitar runs.'Half of My Heart' is featured on Mayer's 2009 album 'Battle Studies,' which also boasts singles 'Who Says' and the Seal-sounding 'Heartbreak Warfare.' To hear the new song, tune into AOL Radio's Lite Rock station.