There are "manifold" devices for adding water to battery cells as needed which may make maintenance of standard batteries easier for your situation. I have read that standard type batteries last longer than maintenance-free batteries.
If you can use a standard lead/acid battery, a USA brand deep cyle battery may suit your needs and cost lots less than maintenance free types. All standard lead/acid batteries require replenishment of electrolyte with distilled water as needed. Also, periodic cleaning of battery cable connectors and other wire connections at battery terminals is necessary for proper 12 volt battery system performance.