Critical symptoms of a weak car battery include difficulty in starting the vehicle, a check engine light turning on, a low fluid level, corrosion on the posts and a swollen battery case. Age affects battery performance as well.
Car batteries are susceptible to a variety of factors that shorten their effectiveness. Taking many short trips does not always give the battery time to recharge, for example. Extreme temperatures also cause a battery to become weak in many instances. Faulty electrical parts or wiring in the vehicle is another possible cause of a weak battery, as is leaving the lights on.