This is a reply sashaw's question:
"Has anyone tried to replace the battery with higher voltage ones?"
Replacing the battery with a higher voltage battery may damage the ICs in the DAC and probably in the Amp too.
DO NOT do this!
If you want more voltage then use an iBasso P4 or equivalent higher voltage portable headphone amp.
Edited by Chris J - 9/20/11 at 4:28pm