yeah this is a shame. I'm still looking into modifying mine to have a separate volume dial and power switch, because I believe it's the combining that causes this issue(though at this point I can't prove nor disprove this)
right now there's 2 firmware versions available; one that just gives you a working DAC, and one that has some EQ stuff going on. as with any device, software updates happen for a reason. better decoding, better compatibility with stuff (say for instance, DSD512). but from the get-go it should sound very good if not best already.
From what i've seen it charges completely, but what is good to know is that the device is always powered through the battery. what this means is that if you leave it charging while using, the power goes through the battery so it charges and discharges continuously.
Having seen how tightly everything is packed inside the enclosure, there really was no other way to have done this. they even had to shave off a corner of the m.2 port!
congrats on your Diablo!