Batteries are designed to last at least one year of NORMAL use. Longer life span can be designed pero mas mahal siyempre. The number of years is not really a good measure of the battery's worth. You have to factor in the electricals, type of engine (mas mainit ang diesel); age of the car (mas old, mas malakas mag discharge due to electrical leakage); at ACTUAL NUMBER OF HOURS USED. May tumatagal ng more than two years kasi mga teo hours a day lang nagagamit. May one year lang kasi almost 8 hours tumatakbo. So iba-iba yan.

Generally, pag hindi mo ginamit ang car for two weeks or more, madidischarge talaga battery. Specially yung mga may alarm, digital clocks, etc.

As for casa supplied batteries, one year lang design pero tumatagal dahil wala pang electrical leakage ang mga bagong cars.