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My name is John and I work for SafeBatteries.com. Perhaps I can shed some light on your question. The number of cycles a battery should last is dictated by the quality of cells that are used inside the battery casing. Most cheaper generic li-ion cell are rated by the cell manufacture for only 300-350 charges, while others like Panasonic offer a very high end cell (type NNP) which is rated to retain about 70% of capacity even after the 500th charges! The average middle of the road cell which most OEM's use in their laptop batteries will last no longer than about 500-600 cycles until they are complete dead. In contracts, most after-market generic batteries, like the ones featured on Amazon, tend to use the lowest capacity cells with very a short cycle life (~300) for cost reasons. They get those eye popping low prices by stripping out service life and power capacity.
Also note the expected cycle life estimated by the cell manufactures also put restrictions on these estimates. For example, along with the cycle life rating, the cell manufacture will state 300 cycles @ 16Wh with a temperature roughly between 50F-120F. What this means is that laptops that require more power to run and generate more heat should expect shorter a noticeably shorter cycle life. A laptop that consumes more than 25Wh of power would probably be considered average to slightly high while 8-15Wh would be probably be considered low power consumption. 22-25Wh is what my Dell E6400 consumes with spikes up to 38Wh if I’m doing a lot.
As for SafeBatteries.com, we specialize making only laptop batteries that are made with the advanced Panasonic NNP type cells. They are widely considered to be the best performing battery manufacture today. They combined some of the highest cycle life and pack more power for longer run times. We think we have a win-win here for consumers and businesses that are looking for a better than OEM experience at a cheaper price point. Stop by and feel free to let us know what you think!
I’m not certain if this is true for all batteries, but I know a MacBook Pro or Air has a battery life expectancy of ~1000 cycles. At that point, capacity is expected to fall to 80% of original capacity, so it isn’t as if the battery just goes belly up all at once. You could still get acceptable performance for quite a while longer. It depends on the specific model/manufacturer, as well as you needs. I’m not sure about Asus, so it could vary quite a bit.