How do know when your battery is on the way out? I check it for water and check the light meter to make sure its charging when the trailer is plugged in .
You won't know really if you are plugged in most of the time. The battery acts as a capacitor/storage in that case. If you are unplugged and it fails to run the slides properly, it is on the way out. Others may have differing opinions, but that has been my experience.