Picked the brains of an auto-electrician last week, as I have been through a lot of batteries, and he reckons todays leisure batteries are not up to what we do. He suggested gel batteries are the way to go, so I am going to try them next.
leisure batteries are normally not designed to go below 20% charge - I don't know where your mate got his info from but it aint right.Jeff is the man to ask about batteries