I looked around, probably got **** in my eyes but I can't find another thread about this so here it goes ..

I connected my N900 to my laptop at work, and it always worked fine as far as I know but today it doesn't seem to be charging at all. It says usb is connected, and it indicates its charging but when I fire up BatteryGraph the "charge" section only says 5mAh at 3502mV, that seems rather low to me ... also if I disconnect it after a while (half an hour or so) it still says 0% charged

I tried different USB ports already, I'll have a try when I get back home to see if it charges on my desktop pc.

Anyone got an idea?

Are you running anything like music And bt headphones. That's when I get the yellow band warning on n900 that more juice is going out than in.
Btw charge output varies on laptops. My Fujitsu/Siemens esprimo doesn't charge half as well as my acer aspire 5738ZG
Cheers!

Did it charge when you got back to your home desktop PC?

Does it charge in your laptop from battery and while plugged in
Some laptops limit charge through USB when on battery to limit drain.

Plug in all your USB ports, not all are powered in a way to provide power for charging items. This is an internal wiring thing, they simply don't always hook up the juice inside and USB is a system of wires and adaptors, not all of which are required for data transfer.

Plug in another device that drawers power, like a portable hard drive (The spinny kind I don't mean flash pens.) Try something that actually draws power. It could be a USB 1.1 power output which isn't putting out the power required for charging. That is why some spinny external hard drives come with a splitter cable, that has two usb attachements to drawer the juice from 2 USB sockets at once. It might be the case for your laptop.

It might say USB 2.0 but you can't tell without looking at wiring again. And even modern computers and laptops don't have all usb ports hooked up to usb 2.0 sockets. Most front end sections are 1.1 for wiring, usb 2.0 for data transfer.

EDIT. I also had an issue of a duff cable. Bought from the internet as a back up as part of a car charging kit. It stopped passing charge of any kind. Had to bin it. So could be the cable itself.