Hi Will,
It is my understanding that the battery should be charging when the XP is turned on. I am unaware of any other means of charging it.
Also, the European site for midis and styles speciffically for GEM (Music Media Soft) is the only one I'm familliar with. I have researched this fairly well and Can't come up with any US sources. However, just for general midis I think there are numerious sites. You might check out some of the other forums and ask the same question. I know there are many sites devoted to Yamaha that offer free midi downloads which should work on the XP. And you know you can convert midis to GEM songs on the XP.
Hope this helps,
Don
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GENOS, Roland FR-8X V Accordion, Bose Compacts.