Because Lithium Ion batteries are finicky things. It really shouldn't be bad after only a year, but it is an HP... So that doesn't help its case. Another thing, laptops require you use the power supply that came with it or a direct replacement, or it won't charge properly. Also, Lithium Ion batteries don't like constant charge-discharge-charge-discharge, unlike older NiCad or NiMH batteries. You generally want to keep it as close to full as possible with few excursions to the 10% or less remaining or they will tend to lose their charge quicker.