I also second ensormeans' answer regarding your battery problems. It sounds like a dead battery. It is very common for old batteries to hold the charge for just a few minutes. Get a new one or three.
however since I charged the battery, now it's working since yesterday without charging (altghough I used it intensively 4hours with wifi and or bluetooth and made 5-6 calls, ...) and the battery is still almost full
I was installing stuff (with the maemo.org applet) and it said "low battery" (normal after 2hrs reading the user contract for OVI even though I won't use OVI and 1.5hr tinkering with the device on wlan+3.5G), so I leaved it alone, it finally shut down by itself.
When I got home I plugged it on a 5V 500mA charger, a yellow light started blinking but after 1hr or so of charging, it wouldn't boot, I checked on the voltmeter, 3.1V, not a normal voltage for lithium battery I think, so I put the battery on a charger I have which is pretty smart but can revive almost dead cells, I let it do it's job all night long and finally, when I woke up a few hours later, the battery was at 4.1V, which is cool, I put it in the phone and it did boot and all, asking for date and suff but it said "low battery" again and
I used it today, worked fine again (but the battery I bought off ebay didn't last long (I'll perform a capacity test with a constant current load when I'm done charging it)), now it's charging flawlessly on my PC with another USB to µUSB cable, I'll check the cable you gave me (thanks anyway), it might be the problem of the phone ignoring the battery or saying "charge problem" or shutting down. but with the new cable: it charges perfectly fine !!!!! so no problem around here.
One software issue: starting the phone - "An unexpected reboot has occurred, your custom kernel settings were not loaded" message appeared. Should be able to solve it by reflashing: http://talk.maemo.org/showthread.php?t=78828