Do you need to replace the batteries in the chime button or the receiver? To change the batteries on the doorbell (chime button) for most Carlon models, you need a ballpoint pen first to remove the chime button from the back. Press the pen point in the small round hole at the bottom of the button. Then gently push in on the tab. Finally rotate the chime button cover up and away from the back cover. Next take the ballpoint pen or a small screwdriver and place it in the slot below the top battery. Lift the battery up. Repeat this with the second battery. Then place the replacement CR2032 batteries into the battery compartment one at a time with the positive side up.
For the most of the wireless receivers, press the center of the brass tubes and lift those free to replace the 4 D cell batteries (2 behind each tube). A few models have a more obvious battery cover for a set of 4 AA cell batteries.
Many Carlon wireless chime manuals are available here: http://www.lamson-home.com/WirelessChimes.php
. The direct link to the manual listed for the RC8800R is http://www.lamson-home.com/ProductSupport/WirelessChimes/RC3304_4300IM_3.06_v2.pdf
I hope this helps.