Car Battery Types and Sizes Explained

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In today’s post I’ll cover the different types of car battery that are there on the market, how they differenciate from one another and the different sizes of car batteries that we can find.

There’s still some confusion around car batteries.

Do they need maintenance?

What’s a deep cycle battery? 

And my favorite:​

I need a new car battery… which one is the best and how do I know I’m getting the right size?

So let’s dive right into it!

​Car Battery Types

There are two main groups of car batteries: Wet and VRLA. 

In the first group we’ll find the traditional old school lead-acid batteries.

Yep, the ones that do require maintenance.

On the second group, we’ll find gel and AGM batteries which offer the best performance (usually at a logical higher price!)

Wet Cell Car Batteries

Wet cell car batteries (also known as flooded batteries) are your traditional lead-acid accumulator.

Specifically desgined for the automotive industry, these are the OG.

Lead Acid Battery

And although I’ve said before that these are the kind of batteries that do requiere maintenance, not all of them do.

Modern day flooded batteries are constructed using a semi-solid electrolyte and are sealed, not needing nor allowing for maintenance or manipulation.

Old fashioned lead-acid batteries requiere some maintenance as they use water and it evaporates because of the temperatures that batteries reach during use.

They need topping-up every now and then and checking with a densimeter for proper charge conditions.

If you ever need to do so, just remember to use destilled water! It’s meant to “hold” the sulphuric acid whilst staying non-conductive by itself, so if you use any other water (like tap water) you’ll damage the battery big time.

Inside this category, we’ll find two popular variations. Deep cycle batteries and SLI batteries.

  • Deep Cycle Battery: Commonly used in marine applications, they are designed to last much longer than any other kind of battery. They withstand charges for a long time and resist being fully discharged multiple times. They amount of power they provide is stable during prolongued periods of time.
  • SLI batteries on the other hand are only meant to do 3 things. Starting, Lighting and Ignition, hence the name. Once they have provided with the power to ignite the car, the alternator takes over and supplies the system. This is the most common type of car battery. They do not withstand getting fully discharged (which is the reason that even if you charge a fried battery and it works 1-2 times, it will fail again until you replace it)

VRLA Car Batteries

AGM Battery

VRLA batteries or valve-regulated lead-acid battery, are sealed batteries in which the electrolyte is held in different ways than traditional batteries. They are sealed, not allowing any gases or liquids to come out.

Ideal for using in small, non ventilated places in which hydrogen gases could be very dangerous.

Storage wise, they are the best and safest kind of batteries. 

Their main strenght is their only downside. It’s impossible to service a faulty VRLA battery.​

Let’s have a look at the two main kinds of sealed batteries.

  • Gel: Sturdy as hell, resistant to impact, shocks, vibrations, hot temperatures, spillage, and electrolyte evaporation. The electrolyte is gelified (hence the name) instead of liquid.
  • AGM: Absorbed glass mat or AGM batteries are designed in a very smart way. The electrolyte is held in glass mats as the name indicates (let’s acknowledge the originality of the automotive industry naming their advances). The glass mats are composed of extremely thin fibers meshed together to form a compact mat in which the electrolyte is held, not being able to run freely inside the battery. They work on the very same way, but can’t be spilled.

Battery Sizes and Groups

Fortunately for users and technicians alike, the car battery industry is all standarized. There are several groups that indicate the size and terminal position of the battery (where the positive and negative terminals are placed)

This makes the job of replacing your dead car battery a much, much simpler task! 

​If you’re looking for a new car battery and you’re unsure of which group (size) is the right one for your car, you can always check with Amazon’s My Garage. Simply entry your car details on it and it will recommend you the right size for your car. 

Side-Post Batteries

Some manufacturers like to re-invent the wheel. Pun not intended, it happened casually.

For instance, GM vehicles side-post batteries in which the cable ends screw to the side of the battery, instead of having the posts on the top of the battery.

GM-Friendly battery groups are 70, 74, 75 and 78.

Recessed Top Posts

euro battery

Eurocar makers do typically place their posts recessed in the top corners of the battery, equalling the height of the posts and the highest part of the actual battery.

Like the one on the left picture, for instance.

Manyfacturers like BMW are fond of hiding their batteries underneath the rear seats, in the trunk or even more random places. I love them despite that.

VAG and other Euro makers typically use batteries have a ventilation system as a part of the battery. The most common size groups are 41, 42, 47, 48 and 49.

American Standard Top Posts

The vast majority of American and Japanese models (as well as other imports) place the top post in a standarized place.

These are the most common battery groups in the US which is likely the kind of battery you’ve seen anywhere.

Groups differ then in height, width or lengh, in most cases height is the main difference, which can lead to installing a battery that’s too high and the posts hitting the hood of the car (all sort of miracles and fun things happen when both posts do, and your fusebox celebrates the 4th of July in all its glory)

​The most common groups are 24, 24F, 25, 34, 35, 51, 51R, 52, 58, 58R, 59 and 65.

Wrapping Up

As you see, there are a few different kind of post placements, sizes and main groups of batteries.

However, if you know the group of your current car battery (it’s usually on the label) you’ll be fine when gear4wheels1-20nt time comes.

I hope this post has served its purpose! If you have any question leave it on the comments below and I’ll be happy to answer!​

Read also: How To Change A Car Battery