hello Toby
battery recommended for the equipment depends on several points.
1 see the capacity of the alternator, never exceed the intensity of it.
2 to change to higher intensity of the battery, replace the alternator for the necessary
well as dry and liquid depends on what you want to use, and droughts are cleaner and you can use in any position
3 if it can be substituted by 75Ah 90Ah, 15Ah always a margin not to saturate the alternator and the regulator does not burn
the duration depends on the same tract that lead.
is worth remembering that the life of a battery depends on the effort required to verify where the same water levels. once dry enough to be sulfated