soldering prob
 

im doin the dual cell mod on my zz, and i got a wire soldered to one of the batteries but i cant get it soldered to the back (flat side) of the other batter.

im using flux cored solder so i dont need flux do i, because that seems to be the problem, but i dont know why it isnt soldering

If you have some sand paper try sanding the face a bit to rough it up. Not too much now just a few scratches and the solder should stick better.

I agree with the above fellow try just to take the shine off it.heast up your iron get it nice and hot.tin your iron( that means to get it hot and then add the solder to it so the iron is covered with solder) Tin your wire (same as above) once both are tinned and your batt is sanded add the iron to the battery and just as the solder is getting shinney/molten add your wire and it should stick fine

Radioshack has soldering tape. Tape that conducts electricity.

ill try the sanding but if that doesnt work the tape it is, thanks guys

I haven't had any trouble soldering to batteries in the past, but you can try an old soldering onto aluminum trick:

Rough up the surface with sandpaper, and put just a TINY bit of motor oil on the metal prior to soldering. (it can be used motor oil)

If that doesn't work then you should start worrying about how many times you're cooking the battery trying to solder to it.