I have an electric outboard motor on my boat. It is normally eleven months before I get back to the boat after a holiday and the battery is still at about 96% charge. One reason that these batteries are popular on large multihull boats, that people live on, is that they can be regularly discharged to about 10% of their full charge with no ill effects. Do that with lead acid batteries and you will shorten their lives dramatically. They are also weigh much less than lead acid batteries which is of interest to live aboard multihull boats which might carry four to eight 120 amp hour batteries.