Open the light lens of the garage door opener.
How to change battery in chamberlain garage door opener.
Connect the red and black wire with the new garage door opener battery.
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Unplug the garage door opener from the power.
Pull the battery out and disconnect the red and black wires from the battery.
If you are replacing your garage door and your existing door opener does not have battery backup you must replace your existing opener with a battery backup opener.
This video demonstrates how to change the battery in your chamberlain universal garage door remote model klik3u.