these may be a deep cycle or dual purpose battery
A deep-cycle battery is a battery designed to be regularly deeply discharged using most of its capacity, unlike a normal starter battery which is designed to only use a small part of its capacity in a short, high current burst to crank the engine.
deep cycle batteries cannot be used to crank start your vehicle, but a dual purpose one can.
there is a trade off between the battery's depth of discharge and the number of cycles of discharge and recharge it is capable of and there is an inverse relationship between these
these deep cycle batteries are generally designed to discharge slowly over 20-100hrs such as with a fridge, and if they are discharged rapidly such as over 1 hour, you will only get to use around half of the usual capacity and the number of cycles will be reduced
none of these lead acid batteries should be fully discharged as this will shorten their life span, and should only be discharged to 20% of capacity at most (usually 50%)
Absorbent glass mat (AGM) batteries handle higher temperatures better, self-discharge more slowly, will charge more quickly (usually within 3hrs from a standard car alternator), have deeper discharge depths, are totally sealed, more robust, do not need topping up with water, can be safely mounted inside a car as they do not need to be vented externally
these can explode if over-charged or their release valve fails (if they have one)
these will usually set you back around $AU230