12V Battery Buying Guide

Find out how to choose the right 12V Battery for your application

When it comes to 12V batteries, a common question is “What is a 12V Battery?”

While there are many types of 12 Volt batteries out there, a 12V  can be classified into 3 main categories:

  • Car Batteries
  • Lantern Batteries
  • A23 Batteries

Car Batteries or also known as automotive batteries, are designed for maximum current output for periods of time to meet the on the spot electrical needs of vehicles to stay on the road. So understanding how a 12V battery works & choosing the right one for you can save you time and money!


12V Automotive Batteries (Car Battery)

One of the most common of the 12V family of batteries, these are commonly found in vehicles to store energy for operating the electrical components that makes cars start and run. This includes the ignition, starter motor and the electric components which facilitate the crank and start of the engine. This is why they are also called SLI batteries - Starting, Lighting & Ignition.

Acting as the main storage and power supply while the engine is not running, car batteries are recharged by an alternator which is driven by a engine belt; while the vehicle is running. This unique design, combined with components such as the negative & positive plates, alternator and reactions from lead oxide, sulphuric oxide & water; generate the electrons that provide the voltage found in your common car battery.

While modern batteries are designed to be low to maintenance free, modern batteries have a inherent weakness in times of deep discharge. Leaving electronics on such as headlights while the car is not running will completely drain the battery. This can reduce the lifespan of the battery significantly or in some cases, the battery will need replacing depending on the battery age. With older battery models you must ensure that battery always has water, as the sulphuric acid and water combination is the main solution that creates the pool of electrolytes that power 12 Volt batteries.

When replacing a battery, connecting the terminal or post; to the right positive or negative post is crucial. These are represented by the + or - symbols, or by a red and black lead. Connecting the wrong posts can cause battery related issues and should be avoided.


Which 12 Volt Battery Do I need?

When deciding what battery best suits your needs, ask yourself these questions:

  1. What size battery do I need?
  2. What is the optimal power output required?
  3. How long do I need this battery for and what is the battery quality?

Checking the standard battery requirements of the vehicle is always a great place to start when choosing the best battery for you.

When it comes to automotive batteries, the main types are:

  1. Starting, Lighting & Ignition (SLI)
  2. Deep Cycle
  3. Valve Regulated Lead Acid (VRLA) Includes AGM
  4. Wet Cell
  5. Lithium-Ion

The most used for vehicles is the SLI Battery designed that is designed to meet the power needs of a car for short bursts until the engine starts and can generate its own power while on the move.  As mentioned, this type of battery is not suitable for deep discharge. 

Deep Cycle Batteries on the other hand, are made for sustained long term energy needs ideal for marine & recreational purposes. This battery type is designed to handle deep discharge cycles of around 80% capacity depending on the quality of manufacturer & the battery make up.

Valve Regulated Lead Acid types are made for low maintenance and need less regular water replenishment as result of being sealed and having minimal chances of liquid spilling out. This does mean that these batteries regularly have to be replaced as servicing them is difficult. This battery family also includes Absorbed Glass Mat (AGM) and Wet Cell batteries. AGM batteries provide more powerful bursts compared to other sealed batteries as result of the fast reaction design of the solution make up & the fiberglass surface mat that gives the battery is name.

Wet Cell batteries are less expensive but require regular maintenance as result of the need to replace water, which makes up the electrolyte solution. This type of battery is less convenient and does not have the longer life cycle of their VRLA counterparts. 

Lithium Ion batteries on the other hand have a higher energy storage capacity with low energy discharge. Manufactured to be lighter than traditional types, these smaller batteries have a shorter life span and in the past were not compatible with large vehicles. This has changed in recent times with some hybrid vehicles being able to operate with these batteries.


Battery Takeaways

When you’re looking to replace or upgrade your battery, consider the above information and always check the standard battery requirements to ensure the compatibility between the two. Choosing the right battery system can mean the difference between being stuck with a flat battery or a enjoyable trip on road or water.   

This is general advice and if you are unsure contact a professional before purchasing. 


Useful Battery Terms

AMP - Is the measurement used to describe a unit of electrical current.

AMP Hour (AH) - A measurement of how much power a battery can store = One AMP for one Hour is 1 AMP Hour (AH).

Capacity - Is the measurement of the single discharge energy amount of the battery.

Charge Rate - The current battery level during the re-charging process.

Cranking Amps (CA) - A common term to rate the on the spot discharge of a battery measured in amps.

Cold Cranking Amps (CCA) - The measurement of the batteries capacity to start while cold. 

Deep Cycle - The voltage cut off level of a battery discharge which utilises about 80% of the battery.


Comments (4)

So which battery?

By: on 5 July 2020
Oddly, No mention of lantern or an A23, battery despite stating them at the beginning. So how do we choose the right one?


By: on 3 July 2020
Amp hours is an indication of the ENERGY not POWER in a battery. A capital "H" is a unit reserved for a magnetic measurement viz. "Henry". Ah or Ahr is the preferred unit. Capacity is usually specified at a defined discharge current - 100 Ah at 20% of capacity [20 Amps] gives 5 hours. Capacity can vary - usually decreases as the current increases. Well done in reducing the confusion for the uninformed,

Hi Arthur and thank you for the clarification on the “H”. I did not understand the significance of the capital letter, We will amend this in future editions and in other material we produce from now on. Warmest Regards Jason

good informatiom

By: on 2 July 2020
This article has good information about various battery types and their service they are best suited to

Hi Ray, Thank you for the kind words, we are working on producing more material like this in order to help customers make informed purchasing and installation decisions in a way that they can understand.

Deep cycle battery preference

By: on 2 July 2020
Hi, thanks for the article. You say " One AMP for one Hour is 1 AMP Hour" does that mean a 135ah deep cycle battery can supply 135 amps for one hour or 1amp for 135 hours or maybe both? Why dont we use a deep cycle battery instead of an sli type battery. Deep cycle charge well and fast, can supply enough current to start an engine and seem to be a much better general purpose battery than the supplied sli type battery. regards Nick

Hi Nic and thanks for your comment. A battery has two capacities. Its “Actual Capacity” and its “Rated Capacity”. So a battery rated at 100Ah would have an actual capacity closer to 130Ah (or even more). The rated capacity is always measured with a constant load. For example, it is common to see a 100Ah AGM with a C20 rating. What does this mean? You divide the 20 into the 100 and it gives you 5. So that tells us that this battery has been designed to discharge 5 Amps for 20 Hours until it reaches 10.5V (which is the international standard for dead). It tells us the amount of load we can run off this battery and the run time that we should expect to see at that load. We could keep discharging this battery all the way down to ZERO and get more Amp hours out of it, but that would be well beyond what the manufacturer would allow/recommend. Most manufacturers say that their battery is flat around the 11.5 to 11.8 Volts (Some higher, some lower). Just keep in mind that battery capacity and performance can be affected by temperature, the number of cycles or the age of the battery and even the size of the load. Crank batteries are very different in construction to deep cycle batteries. they have thinner plates that can give off and receive energy much faster. AGM on the other hand has thick plates, better suited to smaller longer discharges. You can start a vehicle from and AGM but they don’t always like it. This does depend on the type of AGM and the manufacturer. There are models of AGM style battery that are sold as dual purpose. I have been told that some of these batteries have one thick plate and one thin plate. So they have a foot in each camp. Like all things, it comes down to the brand and the model. In more recent times we have seen the creation of the Hybrid or Stop Start battery that is used in many modern Stop/Start vehicles. This is crank battery that is actually closer to an AGM style battery, but be careful using them in older vehicles as it requires a very dedicated charge system. Each year they are finding new ways to squeeze more performance out of lead based batteries. So you never know, one day your idea may just come to fruition. Kind Regards Jason

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