One of the first reasons why a remote stop working is an empty battery. These things are small and do not hold a lot of charge. When the remote is used frequently it can be quickly discharged leaving you outside.
Luckily the fix is cheap and fast and it is definitely a DIY job.
The battery in mine was a 27A 12V battery that I found in my local hardware shop costing about a dollar.
I filmed the entire process and you can check it on the video below. If this was helpful to you then feel free to subscribe to my YouTube channel.