my niece sometimes needs music to calm down, and so far we have found specific versions of nursery rhymes always work ( shes 5 months old), the problem is it means we have to stop what we are doing on our phones to play the songs. 

ive had my eye on these SD card mp3 decoders for a while and thought, hey wouldn't that make a nice custom mp3 player that we can load the songs she likes on.

i found many cases online that use the HW-188 board with usb power, however i wanted one that would run on battery power. the idea being it is a self contained unit that is easy and quick to recharge when needed, and can also be placed near her so she can hear the music with no wires externally.

the battery box i used was one i bought from the range, that was sold as the power supply for an LED light strip, used this one because i had an inline switch.