Batteries... much like everything else under the hood, it is forgotten about until you absolutely need one. There are ways to catch a weak battery before you're stuck with a no-start. A slow crank, corrosion on the battery or even dimming headlights can be a sign of a weakening battery.
Most batteries today are maintenance free meaning you just replace it when it loses its ability to hold a charge. They do generate gases during the charging process and have small vents built-in to relieve the pressure.
Sometimes, batteries can have a leak around the negative or positive posts. We've all seen corrosion on a battery and that is the result of the gases reacting with the battery cables. The gases are basically eating away at the metal of the cables!
I have batteries in stock for most models that carry a 24 month free replacement warranty.