Why do batteries of any electronic gadgets discharge fast after a few months or years?

Thanks for asking me to answer. Battery  requires calibration for optimal lifespan. HP, Apple has dedicated webpages on it. If you are my https://twitter.com/AbhishekCTRL follower or reader of any of my blog, you must have read articles on how to calibrate battery, how to use 85W Magsafe for MagBook Pro. There is a cycle count, after it, dies. Made in China or Made in US will not change the Laws of Physics.  Obviously build quality of the system on chip, battery will matter. Usually a MacBook Pro delivers 5-7 years lifespan if properly used. You can ask any Electrical engineer for non-Mac, non-HP products. Rechargeable battery like from Duracell, should not be used for all products. Here are useful webpages : http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries https://www.apple.com/batteries/why-lithium-ion/ http://h10025.www1.hp.com/ewfrf/wc/document?cc=us&lc=en&docname=c00821536 http://support.apple.com/kb/PH14087?viewlocale=en_US&locale=en_US

Actually, this is the potential limitation in energy storing devices like batteries. Lithium ion or any other chemical combination like nickel molebdenum etc in rechargeable batteries have cells which charges and discharges serially. These cells are made up of layer by layer cathode and anode electrodes, each layer constitutes cycles of charge and discharge.The layers will detiorate after number of cycles due to aging. Their ability to store charge degrades. So, it does happens that way. There are no proved techniques to make battery life longer.