Lipo battery nickel connectors

Builders, Does any of you tried do solder lipo batteries to create pack instead of welding them? They have nicel connectors. My soldering iron and tin are not working. Do you have any hints?

nobody welds Lipos and I am also not sure why you would say they have nickel connectors. On RC packs they usually have no nickel tabs.!

you need special solder to have it stick to aluminium and a lot of flux

thx, i was thinking that this is nicel.