Yup. I left my spare N900 turned on, to see what would happen when the voltage gets too low.

Last time I checked was on saturday. I just had a look now it had turned off. Didn't turn on. Put it on the wall charger I got some quick-flashing in red, like every second or so. After a couple of minutes the led turned solid yellow/orange (more orange than yellow, I'd say). A couple of minutes later it did some quick-red flashes, and then again yellow/orange.

I'll leave it like that and see if/when U-boot shows up (should it turn on automatically when the emergency charging is done?).

Anyway, we definitely need some way of gently informing the user and then turning off the N900 if bme is removed.

Add.: wow. eventually I got a dimmed U-boot, which presumably lead to ACTDEAD mode. I then booted and i2c reported 2831mV (!). Shortly after that the value is around 2930mV.

Question: can the battery (or the N900!) be physically damaged if you let the voltage go down so low? (I realize that an instant shutdown due to insufficient voltage/power may lead to file system corruption. That's another issue which doesn't worry me.)