How long did it last before burning down? I'm asking since I'm using one since august...

i used it on and off for about a year. it burned when i put N800 to charge overnight woke up to the smell of plastic melting.

I'm a new N800 user, having bought one from someone in my lab. He only had a UK charger, and no adapter for Canadian sockets. He gave me a cheapo CA-100 knockoff with it, didn't matter since I have a 5200 phone with charger.

The CA-100 doesn't work well mostly due to its plug (the N800 side), it has to be in *just right* to work - it's very finicky. Neither of my Nokia chargers have this problem (the UK or NA one). So I guess the knockoff's charger pin is out of spec.

Deciding I don't need the UK charger, I cut off the cable and began experimenting. Being in a EE lab with scopes and lab power supplies (capable of controlled current limiting) and knowing a thing or two about power supply circuits I decided to experiment :-) (oh, and a streak of insanity mixed with caution helps)

Executive summary: The N800 is pretty tolerant, but I haven't pushed the limits. Too high a voltage (at low resistance) it will warn you ("Invalid Charger" or some such message appears), this limit seems to be around 7V or so. I didn't push it, and I never let the current go above 1A. Below 4.3V or so it won't take it either.

A note about the Nokia charger: I tested it a bit, too, and found the specs are not quite true, either: It claims an output of 5.0V, 350mA, but on idle the voltage is much higher (up to 8V) but this can drop down to below 5V - and it'll supply up to 500mA. It's a switcher, very non-linear.

I wanted to see if I can build a portable emergency charger, and I now think the best way to do it is a block of 4 standard cells with a 1 Ohm resistor (possibly less, maybe 2 in parallel). I'd expect a voltage between 4.8 (using NiCa rechargeables) to something over 6.5V for fresh alkalines - the charging current of 300-700mA will further drop that over the resistor at the expense of waste heat.

And I think a straight-through USB charger is a good idea. USB is a well-regulated 5.0V. It'll never supply more than 100mA without negotiation (which a dumb cable can't do!) though. So you might never ever see a "Battery Full" sign (which I never have using the CA-100 knockoff) but it'll help you if your battery is running low.

Joe.

Maybe a bad batch then? I use mine as a replacement for the broken plug in the nokia charger (spliced the cable and put an USB female connector), and it's been charging overnight (and during the day) since last august.