My sister has a 2007 V6, a few weeks after buying her car used (about 50k miles) the battery died. She went and bought a brand new battery but about a month later, she was driving on the hwy and her headlights turned off. Just stopped working! She pulled off the rd and turned her car off and it would not start like the battery was dead. Has anyone had this kind of a problem before? I found something online about a diff 07 that's lights would just flash on and off in the middle of the night draining the battery. I had an 05 V6 and over 3 years and replaced my battery once.

 

Have the alternator checked. It is probably not charging the battery properly...which is why the new battery failed after only a month. Alternator failure is not unusual on the 05 - 09 Mustangs.

 

Yeah the shop checked it when they sold her the new battery, that said it was just a bad battery, nope the alternator went out so she had it towed. Ugh... Pain in the butt!