Rick's Free Auto Repair Advice

Buy a car battery

How to buy a car battery

By Alex Steil

Car batteries have a limited life of about three to four years in a typical late model vehicle. So some people change out their car battery every four years whether it needs it or not just to be on the safe side. That’s one approach. Just check the date of the battery to find out how old yours is (see below). Another approach is to have your battery tested once a year at any auto parts store, preferably before winter. Whichever method you choose, once it comes time to replace the battery, here’s what you need to know about how to buy a car battery.

Find out how old your car battery is

If you don’t know how old your battery is, like me, no need to fret! The manufacturers usually put a date code on the battery indicating when it was made. The date may be a numerical code or alphanumerical,  but it’s easily decipherable code. For example, if a battery was made in October 2018, the date code label may say either 10-8 or K-8. Alphanumerical codes are pretty straight forward: “A” for January, “B” for February, etc. One important note, however, is that the manufacturers skip the letter “I” because it’s so easily mistaken for a “1.”

Why type of car battery do you need?

SLI Battery

Older cars and trucks use a traditional starting, lighting ignition (SLI) type of battery. Most SLI batteries sold these days are classified as “maintenance-free,” meaning that you don’t have to regularly check the water level on each cell. Some maintenance-free batteries have a sealed top, while others have removable caps, just in case the battery needs topping off. Neither is “better,” just different.

Vented or non-vented SLI battery

All car batteries can give off hydrogen gas when they recharge. Hydrogen gas is explosive, so in applications where the battery is stored under the rear seat or in the trunk, the battery must be vented to the outside so the hydrogen gas doesn’t accumulate inside the cabin. A vented battery will have a vent port and the vehicle will be equipped with a flexible tube that attaches to the battery vent to move any hydrogen gas outside the vehicle. If your car has the battery located under the rear seat or in the trunk, it’ll most likely have a vented battery. In that case, you MUST replace it with a vented battery. It is unsafe and downright dangerous to replace a vented battery with a non-vented battery. Vented batteries cost more and are harder to find, but don’t skimp on this because you put your safety at risk by buying the wrong type.

AGM or EFB Battery

Some newer cars and trucks with stop/start technology require either an absorbed glass mat (AGM) or enhanced flooded battery (EFB). These batteries are designed to handle many more cycles of starting than a traditional battery. AGM and EFB batteries cost about three times more than an SLI battery. You may be tempted to replace your AGM or EFB battery with an SLI type. Don’t. Using an SLI battery in a stop/start vehicle will kill the new battery in less than six months. In other words, you cannot substitute an SLI battery for an AGM or EFM battery in a stop/start vehicle.

Even more importantly, you must reprogram the computer in a stop/start vehicle when you install a new AGM or EFB battery. That requires a scan tool. So even if you change out the battery yourself, you still have to take it to a shop to have them reprogram the computer. If you fail to do this, you’ll shorten the life of the new battery.

Match battery size and post specifications

Batteries come in many different shapes and sizes, so check your car owner’s manual to find the “group size” and cold crank amp (CCA) rating for your battery. The group size refers to the physical dimensions, (height, width, and depth) and the type and location of the positive and negative terminals. But group size doesn’t include any electrical specifications. We’ll talk about that in a moment.

Depending on where the vehicle was manufactured, the group size is listed as a Battery Council International (BCI) group number, a Japanese Industrial Standard (JIS) group number, or a Deutsches Institut fur Normung (DIN) group number (also known as the German Industrial Standard).

For example, if you own a 2016 Mini Cooper, your owner’s manual may list the battery group size and a DIN H6. However, the U.S. based BCI makes a cross-reference chart that classifies the same battery as a group 48 battery. Either system works as long as you cross-reference.

If you buy the wrong group size for your vehicle, it may not find in the battery tray, or may fit but contact the hood when you close it, OR the battery posts may be in the wrong place for your battery cables. So finding the right group size is critical

Car Battery Electrical specifications

CCA is one of the most important specifications. In general, the higher the CCA rating (within the same group size), the better. The CCA specification in the owner’s manual is the minimum you should buy, but you can install a battery with a higher CCA rating.

Reserve Capacity (RC) is the second most important specification. It refers to the number of minutes a fully charged battery can sustain a designated constant load — usually 25 amps before its voltage falls below 10.5 volts.

If you can find a battery in the right group size for your vehicle but with a higher CCA and RC than the specs in your owner’s manual, that battery would be a better choice.

car battery comparison

Three Group 35 batteries. Two are SLI and have 640 CCA. The third is an AGM type with 850 CCA. See the difference in price and weight?

How old is the new battery

It’s best to buy a new battery from a busy store because their batteries will be “fresher.” Batteries lose their charge at the rate of about 1% per day, so a battery that’s been sitting on the store shelf for six months will be discharged the moment you buy it. The closer you can buy to the date of manufacture listed on the battery, the better. The battery will simply be in better shape once you buy it.

What is a battery core charge?

Lead is a toxic substance and is incredibly harmful to the environment, so it can’t be discarded in the trash. It must be recycled. To encourage you to return the old battery, all sellers add a “core charge” to the price of the battery. It’s simply a deposit that you’ll get back once you return the old battery. Think of it as a financial “encouragement” to be environmentally friendly.

What about battery brands?

There’s are hundreds of car battery brands. In fact, most auto parts stores have their own private labeled “store brands” like; Autozone’s Duralast brand, O’Reilly Auto Parts SuperStart brand, NAPA’s Power or Legend brand, Walmart’s EverStart brand, or Advance Auto Part’s DieHard brand. The actual brand is irrelevant because ALL batteries made in the U.S. come from just three manufacturers: East Penn Manufacturing. Johnson Controls, and EnerSys Energy Products Inc. Each company makes different quality levels and labels them differently for each seller. So don’t get hung up on the brand. Instead, focus on the battery’s warranty as a measure of quality.

What to know about car battery warranties

Car batteries may have a set warranty period where you can get a free replacement if the battery fails to hold a charge during the warranty period. Or, it may have a stepped warranty where it’ll be replaced for free during a set period of time and then incur a pro-rated copayment during the latter part of the warranty. For example, a battery may have a set four-year warranty where it’ll be replaced for free at any time during the four-year period. Or, it could have a four-year warranty where you’ll get a free replacement in the first two years and pay a pro-rated copayment based on the number of months remaining in the warranty.

Which is best? The set warranty is always better. Here’s an example. You buy a four-year pro-rated battery and it fails after 36 months. Even though you bought the battery on sale for $129, the store will pro-rate the replacement battery based on the full retail price of $159. Since you’ve used 75% of the battery’s life (36 months out of a 48-month warranty), you’ll pay $119 for the replacement (75% of $159.99). But if you bought a four-year battery with a set warranty, you’ll get a replacement for free. So a pro-rated warranty simply isn’t as good.

©, 2020 Alex Steil, Rick Muscoplat

Posted on by Rick Muscoplat

Custom Wordpress Website created by Wizzy Wig Web Design, Minneapolis MN