Just what do those month ratings on a car battery mean, anyway?

Dear Car Talk

Dear Car Talk | Nov 01, 2007

Dear Tom and Ray:

Summing up my Saturday:

-- Me (the boyfriend) to Her (the girlfriend): "Your car's not starting right; your battery may be going out."

-- Her to Me: "When you have time, can you maybe fix it, please?" (Translation: "Before you even think about doing anything fun this weekend ...")

-- Clerk (at auto-parts store) to Me: "Yep, your [Autolite 84] battery's almost shot."

-- Me to Clerk: "But I put it in new ... just two years ago. Doesn't the big '84' on the battery mean '84 months' ... as in '84-month (7-year) warranty'?"

-- Clerk to Me: "Sure, but car batteries never last more than two or three years; that's why the manufacturer prorates them so heavily."

-- Me to Clerk: "Oh, sure, I knew that. Just give me another one." (Translation: I'm way too cool to admit I have no idea (A) what's occurring here, and (B) if I'm getting taken.")

So, my question to you on behalf of guys everywhere is: Why do car-battery manufacturers promote batteries as being "84-month batteries" if they seldom last more than 24 to 36 months? And if car batteries aren't going to last more than 24 to 36 months, what are boyfriends paying extra for when they buy their girlfriends "84-month" batteries rather than less-expensive "72-month," "60-month" or "48-month" batteries? -- Gary

RAY: Well, the numbers on the batteries relate to their warranties, Gary. So an "84-month battery" is one that's warranted for 84 months. If it fails before 84 months, it'll be replaced.

TOM: There's a "free replacement period," where the battery is replaced for nothing during the first one to three years (depending on how good your particular battery's warranty is). After that, they'll prorate it, which means they'll give you some money back, depending on how old the battery is when it dies and how much time is left on the warranty.

RAY: And while batteries do vary, in our experience batteries sold by reputable retailers generally last about as long as their warranties suggest they'll last. So a seven-year (84-month) battery usually lasts about seven years. That's because those longer-life batteries have more lead plates in them.

TOM: Almost all replacement batteries sold in the United States are made by three big companies: Johnson Controls, Exide and East Penn. Retailers like Sears or NAPA specify exactly what they want in a battery, and one of those three manufacturers makes the batteries to those specifications.

RAY: Generally speaking, the reputable retailers will order up batteries of sufficient quality to make good on their longevity claims. If you buy a Fred's Battery, Fred may be counting on the fact that by the time his cheap battery dies, you'll have sold the car, forgotten where you bought the battery or been abducted by aliens.

TOM: Now, there are reasons why even a reputable battery may fail sooner than anticipated. A faulty charging system could contribute to early battery failure. But more commonly, frequent short trips, especially with accessories turned on, don't give the charging system enough time to keep the battery properly charged. That can kill a battery before its time.

RAY: And then there's age. An 84-month battery might be new to you, but it could have been sitting on some gas station's shelf for a couple of years.

TOM: That's why it's best to buy a battery from a place that sells a lot of them and turns over its inventory frequently. You also can check for yourself. There are codes on most batteries that tell you the date of manufacture. There's a letter (A = January, B = February), and then a number (7 = 2007). You want a battery that was made no more than six months ago.

RAY: So, you ARE doing the right thing, Gary, by buying your girlfriend the biggest, baddest battery that will fit in her car. You just have to make sure it's from a retailer you trust, that it hasn't been sitting on the shelf collecting dust, and that you're not running your plasma TV off of her cigarette lighter every time she's in the store shoe shopping.

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