Batteries are consumable products they do not last for ever and can only be cycled so many times before they reach the end of their useful life!! Sealed Lead Acid products will last between 2 -5 years depending on its use.
Sealed AGM batteries can be mounted in pretty much any position - Including upside down. This makes them very versatile to be used in a variety of applications. Sometimes to get the right size you can mount this battery on its side.
If you are having trouble searching for your battery - try minimizing the amount of words that you are using. For example if you are searching for "battery for Google nexus 7", trying searching for "google nexus 7 instead" !