This article covers one method of attaching wires to a bare lithium-polymer battery pouch. This could also be done using a battery spot welder, clamping, or screwing.
Step 1: Wire Prep
Before you solder the terminals, plan your wiring.
Where should the battery wires exit the battery? In what direction will they go, and how far? (A scale printout of the layout may help)
Strip and tin the wire ends.
Each bare end should be slightly shorter than the battery tab’s width.