The two tests to preform on a battery to access its condition is a high rate discharge test (really a stress test) the battery is tested under load for a certain period of time under a certain load and the voltage can not drop below a certain voltage. The second test is a hydrometer test which measures charge and acid water density in the battery. A battery may fail if it does not pass either of these tests. A battery may not hold a charge over night if there is a parasitic draw (something staying live even thought the keys are out of the ignition). Charge the battery and leave it disconnected, the following day will it start the car when hooked up? If so the battery held a charge and something is draining the battery and needs to be checked out. A battery will normally last 3 to 5 years, 5 years being an exception.