A 150 Ah (Ampere-hour) battery is a measure of the battery's capacity. It indicates that the battery can deliver 150 amps of current for one hour, or 1 amp of current for 150 hours, before needing to be recharged.
In practical terms, the Ah rating helps you understand how long a battery can supply power for a given load. For example, if you have a device that draws 10 amps, a 150 Ah battery would theoretically last for 15 hours (150 Ah / 10 amps = 15 hours) before needing a recharge, assuming ideal conditions.