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#811
I would say (best guess) is the two big square pads on each battery are the battery terminals. One will be + and the other -. Put a voltmeter across those and see what voltage you get If they are charged you should see around 3.7 or 3.8V. The two yellow wires are likely a temperature sensor to stop the batteries from overheating during recharging. The two large pads will likely trace back to the red and black wires with an ohm meter. What the white and yellow are for I have no idea? See if they go to those other two yellow wires.
The one big caution mentioned with the PowerBoost is, "don't get your battery polarity backwards". If you do bad things will happen, you will more than likely let the magic blue smoke out and it won't work any more. They mention it because a select few of the aftermarket batteries reverse the polarity on the JST plug. Just to be different I guess?