Legislation advises the number of air changes per hour, for example IS:1332 Battery Rooms advises 12 air changes per hour, or suggest that hydrogen concentration levels are kept below 1% to avoid the risk of explosion. You should perform heat load calculation and compare the flow rate as well. The grater shall be taken into account. Please pay attention on the pressurisation as well. If connected to non-hazardous area under pressure shall be maintained. Exhaust shall be separated from other exhaust systems.
Read the relevant codes IEC, NFPA, and IFC.
As defined by IFC 608.6.1, room ventilation:
Ventilation shall be provided in accordance with the International Mechanical Code and the following:
For flooded lead-acid, flooded Ni-Cd, and VRLA batteries, the ventilation system shall be designed to limit the maximum concentration of hydrogen to 1% of the total volume of the room.
Continuous ventilation shall be provided at a rate of not less than 1 cfm/sq ft of floor area of the room.
Exception: Li-ion and lithium-metal-polymer batteries shall not require additional ventilation beyond that which would normally be required for human occupancy of the space in accordance with the International Mechanical Code.
Keep the RH above 30% and below 65%.
Hope the above helps.