I don't drive often, so isolate the battery when she's out of use. I do this because the car draws a small amount of current even when switched off (something to do with the engine management system).
A "popping noise" coming from the battery could indicate the hydrogen and oxygen produced during charging is not being reabsorbed (or vented if it's not a sealed battery). Tiny sparks inside the battery will ignite that very explosive mix! I hope the red vent plugs used for transit have been removed!