Bat houses require annual maintenance and cleaning. The best time to do this is during the winter months while the bats are off hibernating or migrating south. So it is time to pull out that ladder unless you have a cherry picker sitting around your place.
One of the problems with bat houses is that they can become infested with wasps. The good thing is that they are also gone during the winter.
Get a 1/2" dowel rod about three feet long. Tape a good brush to one end (baby bottle brush is an example) and a putty knife to the other end using duct tape. Remember that the chambers are usually 3/4" to 1" so a small diameter dowel and handles should be small so they fit between the chambers.
Scrape out any debris using the putty knife and the brush can be used to remove any left over debris.
This is also a good time to check for any needed repairs or maintenance. Hopefully the repairs are minor and can be completed without taking down the bat house.
Replace or patch any wood that is past repair work.
Use non toxic caulking to seal any cracks or splits in the wood. Secure any loose boards with new screws making sure the screws DO NOT poke through into the chambers and harm the bats.
If the paint still looks good, you could get by with just touching up where you performed any maintenance. Otherwise, give the house a new coat of paint.
It is also important to reinforce the bat house so it is mounted securely for another season.
Your work is done and the bat house should be good for another season.