Specify an Absorbed Glass Mat (AGM) gel type sealed, maintenance free battery designed for use in solar applications. These are non-gassing so enclosure venting becomes less critical to prevent gaseous buildup. These also are not susceptible to freezing, and have a greater lifespan when compared to wet batteries. These batteries can carry DOT, IATA, ICAO, and IMDG approvals so they may be transported by land, sea and air.
The battery should be rated for temperature extremes present in outdoor enclosure, and should carry a warranty that covers a published derate (decay) factor based on age that does not exceed 25%.
The battery can be monitored by the charge controller for optimizing charging voltage based on the ambient temperature.
Always collect the table of discharge rates for the battery chosen. Often times an extended discharge time should be chosen, and the temperature present at discharge should be taken into account when modeling solar panel array size requirements.