Car Battery Types Explained: Groups and Sizes

When it's time to replace your vehicle's battery, you might think that any battery will do. However, there are several car battery types, each with a set of defining characteristics that make each best suited for certain use cases.

These days, batteries are more efficient and reliable. As recently as a decade ago, car owners had to run regular maintenance checks on the battery to ensure that the acid levels were balanced. If there was a discrepancy, the cell would have to be topped-up with distilled water.

Modern batteries are sealed units that lose minimal water, therefore rendering them maintenance-free.

How a Car Battery Works

SLI batteries are the most popular type of automotive battery. They rely on a chemical reaction that occurs when lead and leads oxide plates within the battery container are immersed in an acid solution. This chemical reaction discharges voltage of 6 or 12v, enough to power the starting, lighting, and ignition functions of the car, along with any other electrical requirements.

The battery is connected to the alternator which supplies a continual cycle of charge and discharges when the vehicle is in use.

Types of Car Batteries

Conventional batteries fall into several categories making it difficult to choose the correct one for your vehicle.

Starting, Lighting, Ignition Battery (SLI)

marine starting battery

As the name suggests, this battery is responsible for the ignition, lighting, and successful starting of the vehicle, along with other electrical systems such as the radio and wipers.

It has a shallow charge cycle: The time it takes for the battery to run down, and recharge. It delivers quick and powerful bursts of energy and as such, is the most common type of battery, usually factory-fitted to a new car.

SLI batteries aren't recommended for vehicles that spend a great deal of time standing idle. If this is unavoidable, at the very least the engine should be started once every week.

  • Widely available
  • Powerful energy, supplied in short bursts
  • Maintenance-free

Deep-Cycle Batteries

Unlike an SLI battery, deep-cycle batteries aren't renowned for providing instant energy, rather a sustained charge over a prolonged period.

They are designed to deeply discharge repeatedly and supply a steady amount of current each time. Their ability to do this makes them ideal batteries for small recreational vehicles such as golf carts, and marine vehicles.

A deep-cycle battery can supply a power-surge when requested and also allows the use of electronic accessories when the ignition is off.

  • Longer sustained discharge
  • Perfect for marine vehicles, including boats and jet-ski's
  • Suit some electric vehicles
  • Ideal for golf carts, lawnmowers, and other recreational vehicles

Valve-Regulated Lead-Acid Batteries (VRLA)

All VRLA batteries are sealed units which ensures they won't spill should they be tipped or inverted during an accident.

Since the inside of the battery is not accessible, in the event of their failure, repairing or servicing them is not possible; They have to be replaced. Being low-maintenance is what attracts many buyers as there is no requirement to keep the water levels topped-up.

VRLA batteries work on the principle of internal lead plates becoming the electrodes once suspended in a gel or sulfuric acid dilution.

A chemical reaction occurs, whereby a cell is charged and converts to an electric current.

VRLA batteries fall into 2 further sub-categories;

  1. Absorption Glass Mat (AGM)
  2. Gel Cell

AGM Batteries

Sealed unit batteries that deliver quick, powerful bursts of energy, faster than other sealed battery types. The rapid reaction that occurs between the fiberglass mat and the electrolytes results in a powerful start.

AGM batteries are famed for excellent, lifelong performance and durability with a life expectancy of 5+ years.

  • A sealed unit, no-spill guarantee
  • Powerful start-up
  • Ideally suited to modern cars with sophisticated electrical systems
  • Supply plentiful charge for multiple energy-consuming devices
  • Recommended for 4x4s, large trucks and vehicles
  • Long-life, zero maintenance

Gel Cell

The gel cell battery operates in much the same way as other VRLA batteries, however, some of the sulfuric acid is replaced with silica. This changes the solution into a more gel-like substance that immobilizes and prevents leakage.

It is capable of withstanding vibration, heat, and shock, making it a very durable battery.

However, over-exposure to excessive heat can affect the structure of the gel and reduce the battery's service life.

  • Suitable for a variety of positions due to its no-spill structure
  • Emit little to no fumes, ideal where ventilation is limited
  • Absorb impact and vibrations
  • Their long, deep discharges are perfect for marine and recreational vehicle use
  • Recommended for off-roading vehicles that drive rough terrain and steep inclines

Wet Cell Batteries (Flooded)

As their name suggests, wet cell batteries require an electrolyte solution to supply power.

They work in a similar way to an AGM battery without the need for the fiberglass mat.

Cathode lead plates attach to the positive terminal and anode lead plates to the negative one. The electrolytes, lead, and lead oxide triggers an electric reaction to create power.

The vehicle's alternator recharges the battery after starting.

Wet cell batteries require some maintenance. They need to be inspected at regular intervals, if the level of electrolytes has reduced they should be topped-up with distilled, de-ionized water.

They are durable batteries but are less convenient than VRLA batteries.

  • Inexpensive; often costing half as much as other lead-acid batteries
  • Less likely to be damaged from over-charging
  • Durable

Lithium-Ion Batteries (Li-Ion)

tesla li ion batteries

As the use of all-electric and hybrid vehicles increases, so does the necessity for Lithium-Ion batteries.

They are a smaller, lighter, and more compact version of the conventional lead-acid batteries discussed thus far.

They are capable of storing significantly more energy than a typical battery. However, constant charging to full capacity is known to have a detrimental effect on its life-span, shortening it to around 3-years.

This style of battery works a bit differently to traditional lead-acid models. They require 5-components; cathode, anode, current collectors, and electrolytes.

When charging, the cathode (+) sends lithium ions to the anode (-) via the electrolyte.

During discharge, the operation is reversed. Repetition of this process creates the electric current required to power the vehicle.

  • Designed for all-electric and hybrid vehicles
  • Extremely fast to charge
  • Compact and lightweight

How 12v Battery Power is Measured

The strength and power of batteries are classified and displayed on a label attached to the casing.

The most common output and capacity measurement are Cold Cranking Amps or CCA.

CCA – Cold Cranking Amps

Achieved by measuring the number of amps a battery delivers without dropping below 7.2 volts.

The test is carried out at 0°F for 30 seconds.

The higher the CCA rating, the more efficient the battery is for starting applications, particularly in cold climates.

CA – Cranking Amps

Measured in much the same way as CCA but at 32°F

A high CA figure denotes excellent starting capabilities, particularly in ambient conditions.

RC – Reserve Capacity

How long a fully-charged battery can discharge 25-amps without dropping below 10.5 volts.

The test is performed at 80°F. The result is a unit of time and displayed in minutes.

AH – Amp Hours

The measurement of how long a battery lasts between charges.

Measured over 20-hours, the resulting amount is divided by 20 to provide the AH figure. This number denotes how many amps the battery can deliver for 20-hours.

Therefore, if a battery's ampere-hour is 100Ah, it will deliver 5-Amps of power for 20-hours.

BCI Number/Code

This is the individual identification number stamped on each battery by the Battery Council International and is a way of recognizing the physical characteristics of each battery.

It shows the voltage, dimensions, and polarization (whether the positive terminal is on the right of the left) of the battery. It also shows where the terminals are located, whether they be on the top or the side.

Can You Replace an Existing Car Battery with a Different Type?

You don't have to stick with the OEM battery provided by the manufacturer. Consider the features and factors of all of the car battery types before settling on one.

Check the BCI code on the old battery to ensure you get the correct dimensions. You may opt for a bigger, more powerful battery, which is fine as long as the footprint is the same.

Ensure that any top situated terminals on taller car batteries have plenty of clearance space beneath the hood. If they were to come into contact it would cause the electrical system to short, creating a serious fire hazard.

Final Thoughts

It is always worth considering an upgrade to your automotive battery, however not all car battery types perform equally and are useful for different applications.

If you currently run a gel cell battery, an AGM would not only increase efficiency, but they also have an exceptionally long life expectancy. In fact, AGM batteries are always a good shout for longevity, particularly if you want maintenance free motoring in a vehicle that you expect to keep for a long time.

Richard Reed
I've been a General Manager of a moving company and I've also been a Professional Mover for over 30 years. I've driven flat beds, reefers, dropdecks, moving vans, heavy machinery, etc. In my time as a Mover I've driven over 1,000,000 safe miles. My days of moving and driving truck are past me but The Vehicle Lab allows me to share the knowledge I've gained over the past 40 years.
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