(NAND) boot problems with empty batteries ?

[arne anka]

> are these known problems ?

afaik, yes.

> how can I get the FR up with empty batteries, how to charge an empty  
> battery ?

the way you did.

it is annoying (though i only once and recently was in that situation) and  
i would expect it to be fixed -- other dives shut down if battery falls  
below a certain level, the fr should do so, too.
dunno why it doesn't and never got an answer how to check for critical  
battery state (polling sysfs on my own is no prefered solution, there  
should be some kind of trigger).