[maemo-users] a crank charger is dangerous for 770?

[From: Antonio Orlando]

Today at supermarket they were giving away some crank chargers for  
cellphones, by promotion buying some coffee packages.
So, we've got one of these, it's a little portable plastic thing with a  
crank, a cable and various cellphone adapters.
So nice: I can plug it into the 770 and start charging... :)

My question is: are these gadgets reliable enough to charge my Nokia 770  
(or Nokia cellphones)?
Will I brick the 770 battery if I use this thing enough?

-- 
Antonio