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 (9)


By: on 17 October 2020
I am somewhat confused as under the VRLA description you state that these batteries will need to be replaced regularly as you cannot service them by regularly topping up the electrolyte. However under the Wet cell battery description where you are able to replenish the electrolyte you state these do not have the life span of a VRLA. On one hand you say the VRLA batteries will need to be replaced regularly because you can't service them but then state on batteries that are able to be serviced that they will have a shorter life? Which will be the more economic to use as a deep cycle battery in a caravan over a long term of say 10 years.

tools.com Response
Hi Doug, Unfortunately, we have no batteries that we can categorically say will last 10 years.

amp hour battery

By: on 16 October 2020
Hi, I have a 60w solar panel,want to run a 50ltr brass monkey fridge freezer, also have a battery box, just needing to know what amp hour battery would you recommend?? Thanks.

tools.com Response
Hi John, To answer that question we would need to know how long do you require the fridge to run for and how many amps does the fridge draw ? Best to contact us for more assistance Thanks

Symbols for units of measurement

By: on 16 October 2020
Following on from the comment about capitals in abbreviations for symbols of measurement, H is not just reserved for Henry but also used for Hertz (frequency). The rule is that abbreviations for units derived from someone's name should start with a capital e.g. Hz (Hertz), A {Ampere), W (Watt), V (Volta). Other units start with lower case e.g. h (hour), g (gram). Hence Ah for ampere hours. With prefixes, those for 1 million or more are uppercase; M (mega), G (giga). while those less than 1 million are lowercase; m (milli). k (kilo).

tools.com Response
Hi Richard, Thankyou for the guidance , we will pass this on to the author


By: on 15 October 2020
G'Day Jason, I'm guessing that the 'lantern' batteries' referred to at the start are either Nickel Metal Hydride or Lithium type cells for LED torches. The A23 referred to is a small battery for doorbells, remote controls etc. So is the A27. They are both 12V. They look the size of a shrunken AAA. There are a few little misleading things in the article, but I'm not going to nitpick as this battery business is a subject that if covered in depth takes far more than a quick overview. Anyone who needs advice on batteries should see a specialist. Like most specialist subjects, just when we think we know it all, there's another page to turn. Cheers, Ian.

tools.com Response
Hi Ian, Thankyou for the feedback , we will pass this on to the author

Atem 12 volt 100 ah lithium

10 October 2020
Do you have any reviews or history on this unit , price seems good. Is it suitable under the bonnet as a designated 12 v power source for fridge , acc ?

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