Electronic – Why do 18650 batteries with lesser capacity (mAh) produce higher Amps

The answer is: marketing. Some number, like "1800 mAh", doesn't really mean anything, anyway. At what temperature? At what voltage is the battery considered "dead"? At what current? The charge you can get from any type of battery really depends on these factors, and how far dead you are willing to run it.

All the major alkaline battery manufacturers supply datasheets that specify the capacity of their batteries more completely. This is the place to get capacity information, not the product label.

• Energizer
• Duracell

mAh is a measure of battery capacity, not instantaneous current. A 1000mAh battery can theoretically sustain a draw of 1000mA for one hour before it runs out. Broadly speaking, that means it could also sustain a draw of 500mA for two hours, or 2000mA for half an hour, but in reality battery capacity varies somewhat depending on how much current you draw; lead acid batteries, for instance, have significantly more capacity if discharged slowly.

The product of a battery's mAh rating and its voltage gives a rough approximation of power capacity (in watt hours) - rough, because a battery's voltage will also vary during the discharge cycle.