Just got my N900 today and decided to upgrade the firmware. I got Software Updater and that started to install 44.1, but it's been at the "1 second left" for the last 20 minutes now! Should I be concerned?

Yes. You'd best pull the battery now before it gets too low and starts causing issues. Then make sure it gets recharged properly and retry (or use flasher instead, which seems to be more reliable - see http://wiki.maemo.org/Updating_the_tablet_firmware)

Ok, pulled the battery out to quit the update. Now when I turn it on it goes to NOKIA logo screen and then goes blank/black.

Will try the flasher update instead after leaving it on charge tonight. Is there no battery symbol when the phone is charging? How does it indicate it is fully charged? Weird, as I typed that last bit it has started to make a noise/vibrate a little every 20 seconds or so and the yellow light is coming on and off repeatedly. I assume this is the charging indicator?

Apologies for dumb newbie questions!

That's a bad sign if it's doing that - it means the battery is too low for it to actually boot into the charging mode. Are you using the mains charger or USB?

Normally, when it's charging the LED will just pulse yellow. When it's fully charged it will go green.

Mains charger. The LED is pulsing yellow, but it's a slow pulse. Stays yellow for 30 seconds and then off for 30 seconds. Initially when I put it on charge the LED was just off, probably for about 5 minutes, before it started going into the 30 seconds on/off pulse.

So I tried the firmware update when the battery didn't have enough power? I suppose I should/could have charged it up, but it was showing almost full so thought it would be ok.

If the LED is just pulsing yellow then you're okay - if it's vibrating and beeping then it means it's actually repeatedly rebooting (which is a problem).

And no, you were probably okay when you started the update, it's just that NSU seems to be very flaky (I'd recommend against using it at all), and if the update hangs, the phone seems to go through the battery very quickly.

I should have mentioned it is still beeping/vibrating each time the LED turns yellow or goes off. Just looked at it more closely now and I think it is repeatedly rebooting. The nokia logo screen which is dimmed out in the background goes away and then comes back each time the LED turns yellow to off.

Time to search for the repeatedly rebooting thread!

The problem is low battery - you really need to charge the battery up externally (either in an external battery charger or in another phone).

Don't have an external charger and the other Nokia phone I have (6300) doesn't take that battery. Just checked and 5800 takes it, I know someone who has that, will try tomorrow.

So with the N900 the battery can get so low that you can't charge it up in the phone? That's really poor.

Yes, it's very bad. I'd advise getting a cheap external charger from ebay just in case.