Yes, in many applications you can replace an AGM battery with a lithium battery, but it is not always a simple one-for-one swap. Before changing from AGM to lithium, you need to check that your charging system, alternator or DC-DC charger, wiring and battery installation are compatible with lithium technology.
For caravans, camper trailers, 4WD auxiliary systems, marine applications and off-grid setups, upgrading from AGM to lithium can provide significant benefits including less weight, greater usable capacity, faster charging and longer cycle life.
However, the right battery depends on your application. A lithium deep-cycle battery should not automatically be used to replace an AGM starting or stop/start battery unless that lithium battery is specifically designed and approved for the application.
In this guide, the Power Crank team explains what you need to know before making the switch from AGM to lithium.
What Is the Difference Between AGM and Lithium Batteries?
AGM and lithium batteries may both be used in 12-volt electrical systems, but internally they are very different technologies.
AGM stands for Absorbent Glass Mat. AGM deep-cycle batteries are a type of sealed lead-acid battery where the electrolyte is absorbed into fibreglass mats between the battery plates.
They are widely used across automotive starting, stop/start vehicles, motorcycles, deep-cycle systems, caravans, boats and auxiliary battery installations.
Lithium batteries used in many modern deep-cycle applications commonly use Lithium Iron Phosphate chemistry, known as LiFePO4 or LFP.
LiFePO4 batteries can deliver significantly more usable capacity relative to their weight and are particularly suited to applications where batteries are regularly discharged and recharged.
Can You Directly Replace an AGM Battery With Lithium?
Sometimes, but you should never assume that an AGM battery can simply be removed and replaced with a lithium battery without checking the rest of the system.
The battery may physically fit in the same location and have a similar nominal voltage, but AGM and lithium batteries have different charging characteristics.
Before switching, you should check:
- whether your battery charger supports lithium batteries
- whether your DC-DC charger has a lithium charging profile
- how the battery is charged from the vehicle alternator
- whether the lithium battery has an appropriate Battery Management System (BMS)
- the maximum charging and discharge current of the battery
- whether your existing cabling and fusing are suitable
- the physical mounting location of the battery
- the manufacturer's installation requirements
- any applicable caravan, RV or electrical installation requirements
For a simple portable system, the conversion may be straightforward. For a vehicle, caravan or more complex electrical system, additional components or changes may be required.
Why Do People Upgrade From AGM to Lithium?
The most common reasons for making the change are weight, usable capacity, charging performance and cycle life.
1. More Usable Battery Capacity
A battery's advertised amp-hour capacity does not necessarily tell you how much of that capacity you should regularly use.
AGM batteries are generally operated more conservatively to maximise their service life. Lithium LiFePO4 batteries can typically tolerate a much greater depth of discharge, depending on the battery manufacturer's specifications.
This means a lithium battery can often provide considerably more usable energy than an AGM battery with a similar nominal amp-hour rating.
As a result, you should not compare AGM and lithium batteries based on Ah alone.
2. Significantly Less Weight
Weight is one of the biggest advantages of lithium for caravans, camper trailers, 4WDs and marine applications.
Lead is inherently heavy, so AGM batteries can become particularly heavy when large battery banks are required.
LiFePO4 batteries can deliver comparable or greater usable energy at a substantially lower weight.
This can be particularly valuable where vehicle payload, caravan ATM, storage space or overall touring weight matters.
3. Longer Cycle Life
A battery cycle is one discharge and recharge of the battery.
Quality LiFePO4 batteries are designed to withstand significantly more charge and discharge cycles than typical AGM deep-cycle batteries when both are used correctly.
This makes lithium particularly attractive for systems that are used frequently, such as:
- caravans
- camper trailers
- 4WD touring setups
- off-grid systems
- marine applications
- solar battery systems
4. Faster Charging
Lithium batteries can generally accept higher charging currents than AGM batteries.
For travellers relying on solar panels, alternator charging or limited generator time, faster recharge capability can be a significant advantage.
However, this characteristic is also one of the reasons your existing charging system needs to be checked before converting to lithium.
Do I Need a Different Charger When Switching From AGM to Lithium?
You may.
If your existing charger includes a dedicated lithium or LiFePO4 charging mode that matches the requirements of your new battery, it may already be suitable.
Older AGM or lead-acid chargers may use charging profiles that are not appropriate for lithium batteries.
This is why you should always compare the charger's output and charging profile with the specifications provided by the lithium battery manufacturer.
The same applies to:
- 240V battery chargers
- DC-DC chargers
- solar regulators
- MPPT solar controllers
- inverter/chargers
- alternator charging systems
Never assume that because a charger can charge an AGM battery, it is automatically suitable for lithium.
Do I Need a DC-DC Charger for Lithium?
In many vehicle-based auxiliary battery systems, a DC-DC charger is recommended when upgrading to lithium.
This is particularly important when the auxiliary lithium battery is being charged from the vehicle's alternator.
Lithium batteries have low internal resistance and can accept high charging currents. Connecting a large lithium battery directly to an alternator without proper current control can place excessive load on the alternator.
A suitable DC-DC charger can:
- control the amount of current supplied to the auxiliary battery
- provide the correct lithium charging profile
- help protect the vehicle's alternator
- manage charging in vehicles fitted with smart or variable-voltage alternators
The correct setup depends on the vehicle, alternator, battery capacity and existing electrical system.
What Is a Lithium Battery BMS?
A Battery Management System (BMS) is an important part of a lithium battery system.
The BMS monitors the battery and can provide protection against conditions such as:
- overcharging
- excessive discharge
- excessive current
- short circuits
- cell voltage imbalance
- temperature conditions outside permitted limits, depending on the battery
Power Crank LiFePO4 batteries incorporate intelligent battery management to help protect the battery during operation.
However, an integrated BMS does not mean that the rest of the charging system can be ignored. Your charger, cabling, alternator charging and electrical protection still need to be correctly matched to the battery.
Can I Replace a 100Ah AGM Battery With a 100Ah Lithium Battery?
Potentially, yes, but 100Ah AGM and 100Ah lithium batteries should not be considered identical simply because the Ah number is the same.
A 100Ah LiFePO4 battery will generally allow considerably more of its stored capacity to be regularly used than an equivalent 100Ah AGM deep-cycle battery.
It may also weigh substantially less.
Because of this, some systems may not require the same nominal Ah capacity after switching to lithium.
The correct battery capacity should instead be based on:
- your daily power consumption
- maximum loads
- inverter size
- how long you want to operate between charges
- available solar
- alternator charging capacity
- battery maximum discharge current
A proper power assessment is more useful than simply matching the Ah number printed on your old AGM battery.
Can I Put AGM and Lithium Batteries Together?
AGM and lithium batteries have different voltage characteristics and charging requirements, so they should not simply be connected together in parallel as one battery bank unless the electrical system has specifically been designed to manage the different chemistries.
It is common, however, for a vehicle to retain a lead-acid or AGM starting battery while using lithium as the auxiliary battery.
In these systems, an appropriate DC-DC charger or battery management system can separate and correctly manage the two battery systems.
Can I Replace My Caravan AGM Batteries With Lithium?
Yes, converting caravan batteries from AGM to lithium is a popular upgrade, particularly for travellers wanting to reduce weight and increase usable battery capacity.
If you're setting up or upgrading a touring system, you can also explore Power Crank's camping and caravan battery range.
But a caravan lithium conversion involves more than choosing a battery.
You should check:
- the caravan's 240V charger
- solar regulator or MPPT controller
- DC-DC charging system
- battery cabling
- fuses and circuit protection
- battery mounting location
- inverter requirements
- battery ventilation or enclosure requirements
- applicable Australian installation standards
Australian requirements for lithium battery installations in recreational vehicles have changed in recent years. If you are modifying an existing caravan battery installation, particularly a major AGM-to-lithium conversion, it is worth having the system assessed by a suitably qualified professional.
Can I Replace an AGM Car Battery With Lithium?
This is where the answer changes.
If the AGM battery is your vehicle's main starting battery, particularly in a stop/start vehicle, do not replace it with a generic lithium deep-cycle battery.
Automotive starting batteries are selected according to requirements such as:
- cold cranking performance
- vehicle charging strategy
- start/stop system requirements
- battery registration or battery monitoring systems
- physical size and terminal layout
- manufacturer specifications
A deep-cycle LiFePO4 battery designed for a caravan or auxiliary system is not automatically suitable as an automotive starting battery.
If your vehicle currently uses an AGM starting battery, use the battery specification recommended for your vehicle unless a suitable lithium starting battery has specifically been approved for that application.
Not sure which battery suits your vehicle? Use the Power Crank Battery Finder to search for a compatible battery, or browse our car battery range.
When Does Upgrading From AGM to Lithium Make Sense?
Lithium is particularly worth considering if you:
- regularly use your caravan or camper off-grid
- want to reduce battery weight
- need more usable power without installing a larger AGM bank
- run fridges, lighting, communications equipment or other accessories regularly
- use an inverter
- rely heavily on solar charging
- want faster recharge capability
- cycle your batteries frequently
When Might AGM Still Be the Better Choice?
Lithium is not automatically the best battery for every application.
AGM can still make sense where:
- the existing system is specifically designed around AGM
- the battery is installed in an environment unsuitable for the lithium battery being considered
- the application requires an AGM automotive or stop/start starting battery
- the battery is only used occasionally
- upfront cost is a major consideration
- upgrading the surrounding charging system would make the conversion impractical
The best battery is the one that suits the application and the complete electrical system, not simply the newest battery technology.
AGM vs Lithium Battery Comparison
| Feature | AGM Battery | LiFePO4 Lithium Battery |
|---|---|---|
| Weight | Heavier | Significantly lighter for comparable usable capacity |
| Usable Capacity | More conservative depth of discharge generally recommended | Greater usable proportion of rated capacity |
| Cycle Life | Lower | Typically significantly higher |
| Charging | Slower charge acceptance | Can accept higher charging currents |
| Upfront Cost | Generally lower | Generally higher |
| Battery Management | Generally simpler | BMS required |
| System Compatibility | Compatible with traditional lead-acid charging systems | Charging equipment must be lithium compatible |
| Typical Deep-Cycle Uses | Caravans, auxiliary systems, marine, backup power | Caravans, 4WDs, marine, camping, solar and off-grid systems |
So, Is It Worth Switching From AGM to Lithium?
For many deep-cycle applications, yes.
A correctly designed lithium system can offer less weight, substantially greater usable capacity, faster charging and significantly longer cycle life than a comparable AGM setup.
But the important words are correctly designed.
Changing battery chemistry affects more than the battery itself. Before replacing AGM with lithium, make sure your charger, DC-DC charger, solar system, alternator charging, wiring, fusing and battery location are suitable for the lithium battery you intend to install.
If you're unsure, getting the complete system checked before purchasing the battery can prevent compatibility problems later.
Frequently Asked Questions About AGM to Lithium Upgrades
Can I just swap my AGM battery for lithium?
Sometimes, but not always. You need to confirm that your charger and other charging sources support lithium and that your wiring, fusing, battery management and installation are suitable.
Do I need to change my charger for a lithium battery?
If your existing charger has a suitable lithium or LiFePO4 charging profile, it may not need replacing. Older AGM-only chargers may need to be upgraded.
Do I need a DC-DC charger when changing to lithium?
For many vehicle auxiliary battery systems, a lithium-compatible DC-DC charger is recommended to provide the correct charging profile and control current drawn from the alternator.
Can I use my alternator to charge a lithium battery?
Yes, but the system should be designed to control charging current and protect the alternator. A DC-DC charger or suitable battery management solution is commonly used between the vehicle charging system and the auxiliary lithium battery.
Can I use AGM and lithium batteries at the same time?
Yes, they can exist within the same overall system, for example, an AGM starting battery and lithium auxiliary battery, but they generally should not simply be connected together as one parallel battery bank. The different battery chemistries need to be managed appropriately.
Is lithium better than AGM for caravans?
Lithium can be an excellent choice for caravans because of its lower weight, higher usable capacity, fast charging capability and long cycle life. However, the caravan's charging and electrical systems must be compatible.
Can I replace the AGM stop/start battery in my car with lithium?
Not with a generic lithium deep-cycle battery. Stop/start vehicles require batteries designed for the vehicle's starting and charging system. Follow the vehicle and battery manufacturer's fitment recommendations.
Is a 100Ah lithium battery better than a 100Ah AGM?
For deep-cycle use, a 100Ah lithium battery will generally provide more usable capacity and substantially lower weight than a 100Ah AGM battery. However, battery selection should also account for maximum current, charging equipment and the application.
Find the Right AGM or Lithium Battery
Not sure whether you should stay with AGM or upgrade to lithium?
Power Crank supplies AGM deep-cycle batteries and LiFePO4 lithium batteries for a wide range of automotive, caravan, 4WD, camping, marine, solar and auxiliary power applications.
Rather than simply replacing your existing battery based on its Ah rating, consider how the battery is being used, how it is charged and what equipment it needs to power.
Not sure what battery you need? Use the Power Crank Battery Finder or visit your nearest Power Crank store for help choosing a battery that suits your application.
Battery requirements vary between vehicles, chargers and electrical systems. Always follow the battery, vehicle and charging equipment manufacturers' specifications. Electrical or lithium battery system modifications should be carried out by an appropriately qualified installer where required.