LiPo batteries can only be used about 500 times or cycles. Every time you plug into the mains, regardless if the battery is partly or fully charged, its usually considered a cycle off the 500 cycles (assuming you plug it in for sometime).
Typically, if you plug in your laptop to the mains with the battery everyday, the lifespan of the battery is at most 1.5 years. It starts to degrade very quickly after that.
Some unplug the LiPo battery when using the mains, which can increase the life of the LiPo. It can be a hassle though.
Buying a cheap OEM battery may sometimes offer you less cycles. I suggest a good make and check the manufactured date and cycles. The Shelf life is an important factor too which dictates total cycles available. Cheap ones can be old stock. Be careful.
Cheers,