Welcome to the forums.
It seem weird that two different media players would behave the same way
Are your sure that you music player has done a full scan of your SDcard?
Are your sure that you have the music player looking at the correct folder?
As far as the charging problem goes, when ever I've attached my phone to a device other than my computer, that other device would start to charge itself off of my phones battery. I've never tried to do what you did.
Was your phone set to storage mode? Maybe the tablet was drawing off of the SII.
Have you tried another usb cable to see if that is the problem for the slow charge?