FINALLY found the answer to this:
Yeah, the manual isn't helpful. At all.
I called Treadmill Doctor (www.treadmilldoctor.com) to see what they could give me (I had just gotten a battery from them).
They said I had to take off the side panel, and then the battery was right there.
So, I did it. Here's how.
1) There are about 5 screws that hold the side panels on. If you are sitting on the bike, the panel to your right is the one you are trying to take off. The screws are located:
a) Where the communication port is
b) Around the "neck" that connects the display to the bike
c) In front of where the seat slides
d) At the bottom of the bike on the panel ( this one is hard to find, lay down parallel to the bike, and follow along the bottom, near the wheel, but a little closer to the back)
e) At the back of the seat slider
2) Take off the panel. It comes off, but with a little difficulty due to the pedals. I manhandled the back a little, and then turned the pedal so I could remove the panel in the direction of the arm to the pedal (i.e., moved the pedal up so I could slide the panel up along the pedal to get it off.)
3) There's the battery, about mid way back, by a control panel.
To get it off, there are two screws with nuts on the end holding the battery on. They are on top of the battery. There is a similar-looking third screw on the left side wall, but don't mess with that one. Not necessary.
a) Use either a ratchet or turn pliers to remove the nuts. The front one will be much easier than the back ( mine was located on the front left and back right of the battery). I had to use pliers on the back one because i had no room.
b) Once these two nuts are off, the battery will slide down with the screws still in it and out of the bike. Make sure you disconnect the cables.
4) Put the new battery in.
a) Remove the screws from the other battery, and put them in the SAME spots on the new one.
b) Line up the screws with the holes in the spot for the battery in the bike.
c) Put the nuts back on the screws to tighten the screw in place.
d) Reconnect the wires. The long one is positive (mine was white) and the short one is negative (mine was black). Keep in mind that the battery must go in the same way as the other came out.
5) Replace the side panel.
a) Start with sliding over the pedal, then replace all screws to fasten the side panel back on. I recommend checking the bike by spinning the pedals with your hands once the new battery is in to check to see if it works.
And there you go! Hope it helps!