I was in an aftermarket parts store the other day and a customer said he wanted the largest battery that would fit in his car. The counter person did his job and sold him one; they are in the business of selling parts and making money not giving advice that would result in a smaller sale, on a rare occasion you may find one who will but not usually. The manufactures spend time and money to find the best battery for your vehicle and they do not cut corners here as the demands on the electrical system of today’s vehicles is high and has little room for error. However they do not exceed the demands as this would raise the cost of the vehicle. There is also a space and heat problem with the cramped engine compartments. My wife’s Bonneville has the battery under the back seat, hard to get to, a great idea don’t know why they don’t put it there on a regular basis. The alternator also has a limited output and a larger battery may never obtain a full charge.When buying a battery there are only 2 things to consider. The first is the group number this will assure you get the correct battery for your vehicle’The second is the CCA or cold cranking amps. The greater the CCA the higher the price of the battery. Where I live we can see temps at -40 or more and wind chills in the -60 and it has hit a -100. Not a place to skimp on a battery. The best battery on the market today is the Optima. They come in 3 grades red, blue and yellow and can run in excess of $200, overkill for the average driver. NAPA sells an Exide that is reasonable. GM vehicles owners should also consider AC Delco and for money saving Ever Start is a good choice. I did not mention Interstate or Die Hard as I feel they are high quality but overpriced.The life span of a battery used to be 3-5 years but this is no longer the case. Today’s batteries have been forced to improve along with the demands of the modern vehicle. Also they are sealed and you no longer have to add mineral containing water which destroyed a battery. 7 years would be about the max where I live then I would consider replacement no matter how it tests and heat will destroy a battery quicker then cold. Testing has also improved and no longer is a load test used they are now tested by impedance which is more accurate. Most aftermarket stores will test a battery for free and often also install it at no charge. With the load test they could cheat but the new test equipment it is computerized.