When it comes to powering your vehicle, not all lithium batteries are created equal. Deep cycle LiFePO4 batteries excel at steady, reliable discharge for applications like RV house banks or solar storage—but they aren’t engineered to crank an engine. For that, you need a dedicated starting battery with Cold Cranking Amps (CCA) and thermal tolerance. Our new 12V 100Ah 1200CCA Marine Cranking Battery bridges both worlds on the water, but for automotive engines, WattCycle still recommends a purpose-built starter battery or, at most, using dual purpose batteries strictly for onboard electronics—not for the car’s starter motor.
Here I will take you through a detailed understanding of why most deep cycle batteries cannot be used as car starting batteries. Why is dual purpose battery still not recommended for starting cars but can be used for starting engines on boat?
What Is a Car Starting Battery?
A car starting battery has one job: to give your engine the power it needs to start. These batteries, also called cranking batteries, provide a quick and powerful burst of energy to get your car running. Once the engine starts, the battery takes a backseat while the alternator handles everything else.
Starting batteries are different from deep cycle batteries, which deliver steady power over a longer time. Some people opt for a dual-purpose battery that handles both jobs, but for most cars, a cranking battery is the standard choice. Dual purpose LiFePO4 batteries can also act as cranking batteries, but there are a few things you’ll need to consider before using them this way.
How LiFePO4 Batteries Work as Car Starting Batteries
LiFePO4 batteries fall into two main categories:
- Deep cycle LiFePO4 batteries—designed for sustained power delivery over hours.
- Dual purpose LiFePO4 batteries—engineered to both crank an engine and power house loads.
Only dual-purpose units are rated to start engines; deep cycle cells lack the high-current and protection profile required for cranking and should never be used to start any motor—whether an automotive starter or a marine generator.
When starting an engine, your battery needs to deliver a lot of power fast. LiFePO4 batteries can handle this. But they’re not usually used as car starter batteries, Because the maximum discharge current of most LiFePO4 batteries will not support the start of your car. For example, a small number of LiFePO4 battery BMS support a maximum of 1000CCA for 8 seconds, which fully supports the car's starting current and time, while some LiFePO4 batteries, the maximum discharging current of only 350A can only last for 3 seconds, which is obviously not enough to start the car, when the car has not started, the battery will be broken down by strong current. So you need to carefully check their parameters when buying, but even if you buy a LiFePO4 lithium battery with a large enough maximum discharge current and long enough sustained current, it is still not recommended to use it as a starter battery in your car. Because there’s a other good reason for that: heat. Car batteries are typically stored under the hood, where temperatures can get pretty high. This can affect the performance and lifespan of a dual purpose batteries.
If you decide to use a dual purpose LiFePO4 batteries for your car, it’s important to take precautions, like keeping it out of the engine bay to avoid heat damage.
Key Things to Keep in Mind
Check the Maximum Current: Make sure the LiFePO4 battery can handle the high power demands of your car’s starter motor. If it doesn’t have enough current or power, it won’t work.
Look at the Current Duration: Starting a car isn’t just about the power; it’s also about how long the battery can sustain that power. Confirm that the LiFePO4 battery can handle the job.
Think About Dual-Purpose Needs: If you want a battery that can start your car and also power other devices, a dual-purpose battery might be a better fit. LiFePO4 batteries are great for deep cycle use but aren’t always the best for starting tasks.
By keeping these points in mind, you can decide whether a LiFePO4 car starter battery is right for you. They’re not the default choice for cars, but with the right setup, they can work just fine.
Where Can LiFePO4 Batteries Be Used for Starting Engines?
LiFePO4 batteries aren’t just limited to cars—they shine in other settings, especially where managing heat is easier. For instance, they’re a popular choice for marine cranking batteries. Boats typically have their batteries stored in cooler compartments, making it a better environment for LiFePO4 batteries to perform reliably.
Beyond marine use, these batteries are also great for RVs and backup power systems where high starting currents and deep cycle functionality might both be needed. Their long lifespan and consistent power delivery make them a dependable choice for such applications.
If you’re thinking about using a LiFePO4 deep cycle battery for starting engines, it’s often more practical in environments that don’t subject the battery to extreme temperatures or high vibration
When to Use Dual-Purpose Batteries
Marine Engines (Recommended):
- Cooler compartment environments
- Simultaneous need for starting bursts and trolling motor power
- Cleaner discharge cycles
Automotive Engines (Not Recommended):
- Extreme under-hood heat can shorten LiFePO4 life
- Sustained vibration profiles may stress the BMS
- Dedicated car starter batteries remain the safest choice
Onboard Electronics in Cars (Acceptable):
- Dual-purpose LiFePO4 can power audio systems, camping fridges, and lighting
- Offers longer life and lighter weight compared to lead-acid
- Does not replace the starter battery—only supplements house-load power
Conclusion
For your car, stick with a dedicated starter battery for reliable ignition, and consider a dual-purpose LiFePO4 battery only for powering onboard electronics in cooler compartments. With the right battery in the right place, you’ll enjoy both dependable starts and uninterrupted power for all your adventures.
