system
Given the following post, respond as if you're commenting on Reddit:
human
[MCU] Where/how does Star Lord get new batteries for his Walkman?

And where did get that sweet tape player that he installed on the Milano while we are speaking of "far away from Earth" problems?
gpt
Just because Star Lord didn't come back to Earth and hit up a Radio Shack doesn't mean no one else has. There's a black market for Terran merchandise, as seen when Yondu is shopping. No reason Star Lord couldn't find a tape deck for the Milano. 
As for the batteries, either an alternate power source was adapted. Which would be easy, relative to building space ships and colonies inside a Celestials head, or he bought "primitive" batteries from a trader.