Hiya, the flux I use is called "La-Co regular soldering FLUX paste'. A 60g pot costs £2.25 and lasts forever (unless you use IB4200's that is!). I forgot to mention that I also shrink wrap each cell before putting them into packs. It does keep those labels nice and clean! I do not glue them together though, there is no need to with the method I use to put the packs together and it makes it easier to take them apart if you want to re-match your packs.