How to Find out Battery Size, Where to buy - Northern VA, MD, DC

Hi Roy Thank y ou so much. You'd think this would be a simple question. I want to know the size and specs before I go. The reality -, I have a dead battery so it's not helpful for me to drop by the counter of different shops. I am trying to price compare before going to shops. I have some prices that range all over the place from about 50 at sears to 190 from other places! Due to the economy, I am trying to find how who usually h as the cheapest, is there a "wholesale" parts place nearby that is cheaper that I can use. I have already looked at a number of websites, but I do not know enough to figure if the model they are suggesting is the right one, due to one time, Sears provided me with a tractor battery after puttin in my car information. Oner would think - There has to be a a 'specified battery' size, or model number or dimensions, and other specs pertinent to that car. (It must be on a database at some autor parts places, and must be online somewhere!) I have already looked at the different brands of batteries, the orirignal manufacturers that provide to different places like walmart, costco, napa, autozone, etc. For examplke, I am not in the market for an optima battery but the cheapest I can find, or perhaps a little more expensive iwth an extended warranty. Note this is a 91 Mazda so I'm not going to put in much money. I bought a battery a few years back at NTB for about 65 and now their quote was 125. My local exxon said $110.00. Unfortunately, I can't find the battery price from NTB but I know it has expired. Thanks! A woman who prefers to get this done onlne or ordered and go by and pick it up and one who wants to know all the specs so I am not misled! I have been misled in past due to my lack of knowledge. Alexa