Thank you so much for offering help!
I succeeded in flashing rootfs, I'm soooo glad the battery didn't bail on me!
All my data in mydocs is still there - now do I still need to reflash eMMC?

I restored my my list of apps and settings from backup. Everything seems fine, except UI is a bit jerky. I don't remember though if that's just how the N900 came to me 16 months ago, and I had smoothed things out wit swappolube etc, or if it's actually supposed to be all slick and quick right after a reflash?

Now to avoid this happening again, it seems to me Estel suggested that a problem might have been caused be preset lower voltage profiles? If so, is there any alternative for a non tech-smart user (i.e. I won't be able to fiddle with the settings finding my own perfect profile...)
Thanks for any help offered!