A lot of batteries are called maintenance-free, this one however, really is, if one, more or less, stays within the charging-voltage limits. They can be had in the capacities of 140 and 170 Ah. They can be installed in the vehicle interior, and can even withstand tipping over, in addition, they have a safety device which prevents the ignition of the battery gases.
They feature a bulkier top cover with various channels, in which the developing gaseous substances are absorbed. If these do manage to escape, then on the opposite side to where the terminals are, this is why the terminals are both on the same side.
In the channel, where all the upper parts of the cells are grouped, there may be small plates built in, which serve as seperators. The gases can also be directed past components which are susceptible to corrosion by means of a flexible, thin hose. In any event however, the battery is protected against gas escaping, through pressure relief valves.
This complicated system of guiding the gases does of course, have it's limits, if one recklessly uses an outdated battery-charger to exceed the last 80 percent. This can, even with this type of modern battery, cause it to explode. 09/10