What is the Group Size of a Car Battery?

Unfortunately, flat batteries happen to the best of us. A battery is a perishable bit of kit and, although it’s the lifeblood of all the electrical systems in your car, it will need replacing sooner or later.

Some batteries are built to higher qualities and last longer than cheaper models, but all of them will begin to fail over time.

In this article, we aim to go through the group size of a car battery, as well as what you might need to know if you’re thinking about changing the battery yourself.

Signs of a Battery Failing

If your car’s battery is starting to fail, you may notice one or more of the following symptoms:

• The car will struggle to start, particularly on cold mornings. The engine will crank for longer than usual. That’s the noise the engine makes when your car is turned to “start” in the ignition. You might need to press the throttle pedal to engage the engine in this situation too.
• You might hear a “click” sound rather than the usual sound of the car starting. Usually, when your car starts, the starter motor engages its pinion wheel with the flywheel of the engine. The motor then causes the pinion wheel to spin, which turns the flywheel and enables the engine to start. It’s the equivalent of when, on very old cars, they had to stick a crank handle in the front of the car and give it a spin to start it. This click is the sound of the pinion engaging, but due to the lack of battery power, it doesn’t spin. It’s the equivalent of putting the crank handle in the car but then not being able to turn it. The engine won’t start in this situation.
• Electrical components might not be functioning at their usual full capacity. The most obvious one to see for this is either your headlights or interior lights that are not as bright as you feel they should be. If your headlights are clean, the cause of this dullness could be a failing battery.
• There could be misfiring and backfiring. The battery sends a charge to the spark plugs to cause it to fire – this gives the engine its life. The spark plug sparking causes the air and fuel mixture to ignite, forcing the piston downwards. The crankshaft then translates this movement into rotational energy, which is sent to the wheels and used to power belt-driven parts of the engine, such as the alternator or air conditioning compressor. When the battery isn’t putting out as much power as it should, the spark plugs won’t always spark (misfiring). This will manifest itself as a loss of power and an imbalanced engine as you look at it. This can lead to a build-up of fuel inside the cylinder, which may detonate at the wrong time (engine knock), or mix with another load of fuel and cause a particularly strong detonation. This strong detonation can cause the car to backfire. Backfiring doesn’t necessarily mean there’s a problem with your battery, so watch out for that.
• If you see any physical signs on the battery that it’s failing, such as cracks or leaks, replace it immediately. Be very careful as you do so you don’t get any of the battery fluids on you. If the battery is breaking, it’s either because it’s not holding a charge well, or will soon be in that state.

A Quick Note on Battery Testing

Although the battery may be a problem, sometimes there is a much deeper root cause.

For example, the alternator may be on the way out. The alternator is attached to the auxiliary drive belt and works as a charger for the battery. It’s a bit like leaving your phone plugged in while you use it. In theory, it never runs out of charge. If the alternator isn’t functioning properly, you are likely to notice if the battery is flat.

It could go deeper still. There could be a problem with a tensioner on the drive belt, which means the alternator isn’t spinning properly. This could be what has caused the battery to begin to fail.

Although replacing the battery may be necessary, it’s not necessarily the root cause of your problems. For example, if there is a problem with your alternator and you only change the battery, you will find your new battery to be in the same state as your old one before long. You would need to fix or replace the alternator as well.

Battery testers come into play to avoid getting stuck in situations like this.

You can purchase your own, or take your car to a garage who will do it for you. Battery testers usually test both the battery and the alternator, so you can begin to see where the real cause of the problem is for your car.
Paying out a little extra for this test could save you lots of money in the future, so it’s worth it.

If you decide to get your own battery tester, make sure it comes from a reputable source. If something goes wrong when you’re messing around with electrics, it could be a potentially expensive or deadly mistake.

Choosing a New Battery

If you decide to replace your own battery instead of taking it to an auto shop, that’s great. It’s vital to get the right type of battery for your car. You can find this information in your vehicle handbook or by using an automotive database and entering your registration plate online.

Many stores and their websites will be outfitted with these databases, so they will be able to get you the right battery for your car that way. This can save a lot of time, but you should always compare it with your vehicle handbook and the battery that’s already installed.

You will need to check these things:

1. The group size
2. The battery type

All car batteries run off the same voltage: 12 V. When a car is running, and the alternator is generating power, you will see a slightly higher reading of up to 14.4 V. At rest, though, all batteries should technically have an output of 12 V.

Group Size

The group size is a standard within the industry for the literal physical size and shape of the battery. Different manufacturers tend to sue different group sizes, but they tend to be fairly consistent across all their models.
The group size standard describes the dimensions of the battery (height, width, and depth) as well as the locations of the terminals. These might be on the side or on the top.

To find the group size of your battery, look at the label on your previous battery, your owner’s manual, or online.

Some examples of group sizes include 24F, 51, 51R, 65, or 74.

Battery Type

There are two types of car batteries: wet cell and VRLA.

Wet cell batteries are filled with a liquid (technically called a “flooded battery”). This liquid is a type of lead-acid, and functions as an electrode.

There are two further categories within wet cell batteries: SLI (starting, lighting, ignition) batteries and deep cycle batteries. VRLA (Valve Regulated Lead Acid) batteries, by comparison, store a set amount of electrolyte in the form of either an absorbent glass mat (AGM) or a gel.
Again, you will find this information in your vehicle handbook, on the previous battery, or online.

A Final Word of Warning

Having the correct group size for your battery is imperative. If you get the wrong size, the best-case scenario is that it won’t fit. In the worst-case scenario, the terminals of the battery could make contact with the underneath of your car’s metal hood, causing a spark and potentially a vehicle fire.

Conclusion

If you decide to change your battery yourself, be careful. Cars can be fiddly things. However, done right, changing your car battery – making sure the group size and battery type are correct – could save you a bit of money.

As always, if in doubt, please take your car to a professional. They will do it for you in no time.