Originally Posted by
lexyp
lead solder rosin core (standard stuff). 60w iron on full. basically the same combo i usually use on 10awg wires, but wouldn't work in that particular circumstance on a thin wire for a 250mah lipo. didn't try to break up the threads...maybe do that next time.
Your soldering iron is too hot. Oxidation happens faster at higher heat and you're burning the flux, preventing it from doing its job. I'm assuming your iron has an adjustable temperature because you said you use it on full. Set your iron for 550˚F to 600˚F (290˚C to 320˚C).