smart charger from halfords, 2 leisure battery,s, one or the other always on charge,
i rotate them put fresh one in van before work , take the one out from the day before and put on charge,
with a smart charger it can be left on charge for weeks, as it swithches to maintainance mode when battey is charged , and will alternate between charge/maintainance mode.
both my battery's are over 2 years old -still going strong

daz