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.
Step 2: Tab Prep
Peel back one of the battery terminals.
With a small file, roughen the outer half of the battery tab.
Fold the end of the battery tab over, to create a small ‘hook’.
It should be just large enough to fit the wire in.
Put a tiny drop of flux in the hook.
You can spread it around with a piece of wire.
Step 3: Soldering
Place the wire into the hook – making sure it matches the polarity – and press it closed.
It may help to clamp a little bit of the insulation in the hook as well.
Carefully, press the soldering iron against the folded hook.
The aim here is to heat up the tab, the wire and the flux, without heating up the battery.
If the battery near the tab is warm, stop and wait 2-3 minutes before attempting again.
Run the solder into the folded hook until it begins to melt and ‘wet’ to the metal.
As soon as it seems that a good contact has been made, stop. The solder should have bonded well to both sides of the hook, and to the wire as well.
Step 4: Tidying
Roll the tab up until it is inside the battery sled.
Replace the covering tape.
Repeat for the second battery tab and wire.
Step 5: Finish Up
Once both tabs are soldered, the wires can be fixed in place with hot glue, and the area covered with a small quantity of masking tape. Complete!