@ mr_nobody,
Interesting you should mention the card episode.
My notes from this afternoon:
"Tried with wifi on [waking from sleep]. -->OK.
Noticed it said battery is charging even tho it wasn't. Turned off wifi. Battery at 20% & wifi using most of it. Put to sleep, woke it up. Tried to open apps, said SD card unexpectedly removed. (It wasn't.) Then became unresponsive. Tapped power button. Went black. Did 10s reset. Booted up OK. Powered down to recharge."
I used the Vox and read for a bit after the last startup, before shutting it right down to recharge. The green light indicating full power came on in about 2 hours. I haven't powered it back up yet. (I was busy with other stuff, including browsing the discounts on the Kobo site, using my laptop.

)
My Vox doesn't seem to like being put into sleep mode with the wifi turned off.
My unprofessional diagnosis--a power management conflict involving the wifi. Maybe if I want to conserve power I should shut down the wifi while I'm using the Vox unless I actually need the wifi on and then just make sure the wifi is on before putting it into sleep mode.