because you always use your laptop with the power plugged in.you HAVE to use a laptop on battery alone to keep the battery able to take a charge,batteries LOVE being run down to virtually empty.
predominately using any rechargable device on mains power will kill the battery.
As has been said above. Do not use it plugged into the mains with the battery still inside, pop the battery out if you're using the mains. Let the battery run down to nothing, or very, very close to nothing, before you recharge it. It'll keep its life for much longer.
All the points about battery lives i don't think apply anymore. Lithium-ion batteries don't require running down to nothing, I think. I could easily be wrong, i'm going on year 10 science lessons here.
I'd go for the cheaper option as it will be fine in the short-medium term and then you can simply buy another if it starts to loose charge in the (distant) future.
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