I think most of us know this handy test. But still for those of us who do not know, here it is:
We can test remotes or get an idea of their battery strength using a mobile phone camera.
Just turn on the mobile camera, point it to the Infra-Red (IR) LED of your remote and press any button on the remote.
You will see a bright white spot if the batteries are strong, dim white spot if the batteries have gone weak.
You can test whether remotes are working or not by installing new or fully charged batteries and doing this.