Yesterday i had some problems with my USB Conection.

The Battery was empty. Nothing new, happens quite often. ;-)
I usualy charge the Phone via USB on my computer. But when i put it in this time, strange things happened.
The LED startet to indicate normal charging for a minute or so, my PC detected a new device. Then, after a minute or so, the LED went of and the PC detected disconecting of the device. I did nothing. 30 secs later, normal flashing and PC detected conection again.
I wasnt able to start the Device, it seemed as if the Battery didnt get charged at all.

I did the usual testing, using an other USB Port, using a powered USB-Hub (The N900 draws quite a lot of power from the USB Port), turning the device on (the Nokia-Logo appears, but due to a lack of electron ind wont do much more) and conecting it, trying to boot it when conectedc (the Nokia Logo appears without backlight) and things like that.
Nothing worked

I had to use the standart-charger to charge it a bit. After i was able to boot there were no further problems. USB worked flawless, charging via USB was possible again.

Now, my question, is this a Bug? Anyone seen this before? Can it happen AGAIN? Does it indicate some kind of Hardware Failure?

yeah it seems when the battery is dead. usb outputs a lower voltage than a socket charger. ive had this problem."failed to charge insuficient power"

i wouldnt worry too much i think its normal.

the "failed to charge insufficient power" is because the N900 is one of the few devices really following the USB - Specifications. It NEEDS the System to allow high power consumption (wich is why it doesnt work with most dummy-chargers btw)
If the System isnt booted or fails to respond fast enough to the N900s request for high power (or something else in the communication doesnt work), it wont charge.
But thats something different i think. Anyway, ive charged a completly empty battery with the USB Charger several times without any problem.

It is not a bug and not just happens with the N900.

When the battery is too low and the charging current is too low, the electronics inside the battery does an emergency shutdown to avoid further capacity loss (when you plug-in the charger, the device boots up and for a short time it uses maximum power witch causes the problem).

When the battery is completely discharged (no i don't mean to 0V or such) then the recomended way to bring back your device alive is to use a high currency charger.

Yeah, i know. Had it with my mobile sometimes due to a software bug (its a sony-ericsson).
The battery wont respond to anything for a while. It is to keep those Li-Ion / Li-Poly baterries from exploding...

But i was still able to press the powerbutton, the nokia logo came up an when no charger was conected even the Backlight went on! So no *completly* dead battery.

And, as mentioned, the device seems to charge for a minute or so (with the nokia logo on screen, but no Backlight) and then seems to do kind of a reboot. The PC even recognices the device as conected, so some parts seems to be booted up.

Maybe this is because of some kind of mass storage handshake?
The part where the logo is shown without backlight is where you can/have enter(ed) R/D mode for flashing. So USB-connectivity should just fire up there.

Windows has a power save option for USB devices. This may be turned off via device manager or advanced power settings and may help you.

My guess would be:
- device connected
- usb init with pc -> charging
- pc notices that your n900 is not used / no mass storage available and turns it off to save power
- n900 shuts down due to insufficient power / charging

Good guess.
i never had this problem before (on the same PC, same config etc) but who knows what Windows does.
I also think its some kind of communication issue. What is still strange is that the "cycle" is rather slow (the Nokia logo appears almost immediately and stays there for a minute or so. The LED is flashing the normal way before the problem starts). That would indicate a power save mode (not used for a minute -> deactivate high-power-mode -> The N900 then starts the cycle again, requesting high power. If the N900 is fully booted (when plugged in charged) it does provide some functions, therefor isnt disabled by windows powersaving)
i have deactivated all power saving functions (The PC is equipped with a Rev A Geforce 280, therefor the only way to save power is to turn it off) but it could still be that something passed my attention. i will look into that...

Second guess (if your battery was REALLY near dead):

- n900 power on
- charging start
- n900 disconnects usb due to poor hw drivers (yeah, ask the USB Host mode dev. team about that xD ) and wants to initialize it later again
- it doesn't do so, because it notices that your battery is dead and there won't be enough power to boot up
-> shutdown

Third guess:
- n900 power on
- charging start
- n900 offers mass storage and device handshake to pc
- doing so consumes much more energy than available
-> shutdown

So there are a lot of possibilities why this happens. I would guess this is a "normal failure procedure" and you don't have to worry about.
Wall charger and USB charging on PC incorporate different usb plugs. The wall charger has short circuited center pins afaik, so this may be resulting in a different behaviour when charging near dead.