You will need to remove the plastic covers from the body of your Cybex 500R exercise bike. You will find the battery located in the center of the bike frame between the front and rear of the bike. It will be near the lower circuit board and will be bolted to the frame of the bike.
You will need to remove the plastic covers from the body of your Cybex 500C upright bike. You will find the battery bolted to the frame near the alternator at the front of the bike (between the front leg and the crank pulley).
How to Replace the Battery on a Cybex 500 Bike:
Once you've located the battery on your Cybex 500 bike, you will begin the replacement by disconnecting the battery from the lower board.
Using a Philips screwdriver, remove the screws attaching the battery to the frame.
Remove the battery and install the new battery in reverse order.