I don't see how the sd card helps in this case. I like to be able to scan through my sounds on the MP3 if I need to change it and sometimes with birds over head if they hang up. I'm not sure how you could do that without opening up the box and then maybe not even then. 2 inexpensive MP3's that can be charged from the 12v in my pickup always has me in the sound game. a fully charged MP3 will run pretty much all day anyway...the battery for the amp is the bigger issue.