X60S Extended Battery Lifespan - How Long?

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My 5.2 amp extended battery died a couple days ago. I bought my X60 22 months ago and use it everyday both with and without the A/C adapter. I use the setting for battery optimized. I would hate to take it out of the computer everytime I used the A/C. One person on another forum suggested the battery might be good for 500 discharges and charges. At one a day, maybe I did better than average but a replacement is painful ($165).

With daily use, and the battery plugged in, what have been your experience? Thanks in advance.

rg