If your battery (including “Sealed” or “Maintenance-Free” ones) has small holes at each side or on the top, these are for venting battery gasses and must be connected to the tubes.
During normal charging and discharging, some gases escape via valves and the vent holes. Maintenance-free just means that most of the gasses generated by the charge/discharge cycles are re-combined within the battery and you don’t have to top-up the electrolyte. In normal operation some gases escape via pressure-release valves (vent holes). Even fully-sealed batteries have emergency valves to prevent over-pressurisation in fault conditions. These gases are acidic and potentially explosive, so if a battery is located in (closed) passenger/luggage compartments (like the NA and NB MX-5s) rather than the (open) engine bay, the gases must be vented to the outside.
A new battery will likely have transit plugs fitted.
Google “car battery vent hole” and “car battery maintenance free”. if you want more info.