now , for the soldering part , u will need some thick tip
high power solder iron.
dont use something like 20W solder iron!
those batteries dont like heat too much , u wont see any physical damage on the cell , but if u heat them too much , the capacity of the battry will be lower then nominal .but dont worry about that too much , it will still work
unfortunately ,i was too lazy to get a bigger solder iron , so i used my hakko , which is 130W (i think) but the tip was too thin , this made the soldering very ugly and i heated the batteries too much , i think . i have no patiance most of the time
after each soldering , i put the batteries on my air conditioner to let them cool quick .
u will also need solder flux , and solder obviously.
put flux on anyhing u are soldering , this will make it a bit easier and the solder will stick better to the alu cells.
this is the iron my lazy ass used.