Flip the battery unit over, taking special care to not lose the insulators that will come loose (annotated with red boxes).

Rotate the battery unit 180 degrees so the main leads are closer to you. These can be found as shown in red circles.

Use a multi-meter to probe the voltage across the two large solder pads to see just how low voltage your pack is at. The positive lead is on your right and the negative lead is on your left when looking at the pictures with red circles

I initially read 6.85V on my battery pack. Take note of this voltage for the next step.