AA batteries suck, LiPo’s are cool. The below video shows you how to mod the FPV1 so it takes a 3s LiPo rather than AA batteries. (This isn’t really a mod but I thought it might be useful for someone).
I’m not sure if the FPV1 has a JST connector for the battery I think the below transmitter is the advanced transmitter for the 501 (I have a H7000). If yours doesn’t just take the back off, unsolder the battery lead and solder a JST connector in its place.