Should have direct vented the battery compartment outdoors.
There will be some venting for the whole room, but that's a later project. Need to build a HRV system. (premade ones are WAY too expensive) If I just direct vent it will get too cold in there, and that's not good on the equipment or the batteries. If you exhaust air, you need to replace that air, so there will be an intake and exhaust.
I'll be putting a h2 sensor though to be safe. I don't anticipate much hydrogen being produced as it's a standby system so the batteries only really run at float levels and very low current.