Hmmmm...
Depends on the type of lead acid battery. 'Leisure' batteries are designed to be charged and discharged slowly and can be discharged almost completely without damage. A long float at under 14 volts seems a good compromise between not-quite full charge and overcharging.
Starter batteries can be charged and discharged fast - eg in a car by a high output alternator - but they don't like deep discharges.
regards
Allan