When the remotes don't work very well, the batteries 3V CR1620 may be drained too low. We need to check the batteries and replace if necessary. To open the case, get a small screw driver or you're strong enough, you can pull the case and the remote apart.

twist the screwdriver... ... 90 degrees firmly to pry the case off the remote, carefully.

Use two hands, 2 thumbs to pull the remote case on the side apart to expose the batteries and the circuitry.

Batteries and circuitry

There are 2 batteries on top of each other, use DVM to check the voltage, it should be 6.1V, the ones that are weak or don't work measured 5.6V

Remove batteries and replace with new ones (2)

Make sure the + side (flat side) is on the bottom and both of them sit in the case fully. Close the case, it's time to check the remote to see if it still work, it should work with out the need of reprogramming. But in case of a new ebay remote with bad batteries, we need to program the remote as follow