These are small Sealed Lead Acid batteries that are generally used for semi-portable appliances that need more power or a fair bit of power (more than can be provided by D, C or AA cells) for a longish time. They are typically used for people who go caving, or for lighting for an overnight camping trip where you are travelling on foot. They are not ridiculously heavy or bulky. They are good to drive a lantern on a tinny for that night fishing expedition. Being sealed, you cannot fear that the battery acid (which is actually a GEL) will spill. The amp-hour rating tells you how long the battery will last before it goes flat. For example, a 7.2Ah battery will give 7.2 amps for one hour or 3.6 amps for 2 hours or 1.8 amps for 4 hours, etc. Generally an adequate amount of current for a lantern. They are ideally charged by solar panels.Also often found in alarm systems, NBN installations, and other critical systems with backup batteries.