When drivers search for “24F vs 35 battery” or “difference between 24F and 35 battery”, they are usually standing in an auto parts store, trying to decide which battery to buy. The old battery label says 24F but the shelf is full of Group 35 batteries, or vice-versa, and it’s not obvious whether they are interchangeable.
Both 24F and 35 batteries are 12-volt automotive lead-acid batteries defined by the BCI group size system. The group number does not represent voltage or capacity. It mainly defines the external dimensions and terminal position so the battery fits correctly in a specific tray.
This guide compares 24F vs 35 battery size, weight, CCA and typical applications, and then explains when it is safe to swap between them. We will also answer common worries such as “Will a higher CCA damage my car?” and briefly show when you should stop thinking in terms of starter batteries at all and move to a LiFePO4 traction pack for electric drive.
Quick Answer: 24F vs 35 Battery at a Glance
In most product families, a Group 24F battery is physically larger and heavier than a Group 35 battery, and often offers slightly higher CCA and reserve capacity. It is better suited to vehicles with higher electrical loads or colder climates where extra cranking margin is helpful.
A Group 35 battery is smaller and lighter, which makes it ideal for compact engine compartments and vehicles that were designed around this footprint. In mild climates and normal use, a good Group 35 battery will start the engine just as reliably as a 24F.
Table 1 – Key Differences Between 24F and 35 Battery
| Feature | Group 24F battery | Group 35 battery |
|---|---|---|
| Typical dimensions (L×W×H) | ~10.3″ × 6.8″ × 9.0″ (approx.) | ~9.1″ × 6.9″ × 8.9″ (approx.) |
| Footprint & volume | Larger, takes more tray space | More compact, fits tighter engine bays |
| Weight (typical) | Heavier | Lighter |
| CCA range (same series) | Often slightly higher CCA | Slightly lower CCA but still meets OEM spec |
| Reserve capacity (RC) | Usually higher RC (longer runtime) | RC a bit lower |
| Typical usage | Vehicles with more space and higher electrical demand; colder climates | Compact cars and crossovers; mild climates |
| Swapping potential | May replace 35 if tray and hood allow | May replace 24F only if tray, hold-downs and cables still work |
Exact specifications vary by brand and model, so always compare the datasheets of the specific batteries you are considering.
What Does Group Size Mean for 24F and 35 Battery Types?
Before comparing 24F vs 35 batteries, it helps to understand what these numbers mean.
BCI Group Size Basics
BCI (Battery Council International) defines a set of standard case sizes for automotive and marine batteries. A group size describes:
- Approximate length, width and height of the case
- Terminal type and position (left / right positive, top posts, etc.)
- The general mounting space vehicle manufacturers design around
Group size does not directly specify:
- Battery chemistry (flooded, AGM, EFB, etc.)
- Amp-hour capacity
- Exact CCA or reserve capacity
So a “24F battery” simply means “a battery built to the 24F case standard”, not “24 amps” or “24 volts”.
Where Group 24F and Group 35 Fit in the BCI Family
Both Group 24F and Group 35 are medium-size 12 V batteries commonly used in passenger cars and light trucks, especially from Japanese and Korean brands. Nearby you will see sizes like Group 24 (without the F), Group 27, and Group 34.
Mini Table 2 – 24F and 35 vs Other Common Group Sizes
| Group size | Typical L × W × H (inches) | Notes |
|---|---|---|
| 24 | ~10.3 × 6.8 × 8.9 | Similar to 24F but slightly lower height |
| 24F | ~10.3 × 6.8 × 9.0 | Focus of this guide; used in many sedans & SUVs |
| 35 | ~9.1 × 6.9 × 8.9 | More compact; common in smaller vehicles |
| 27 | ~12.1 × 6.8 × 8.9 | Longer; used in larger vehicles & marine |
Again, dimensions are approximate; always confirm against manufacturer data.
Physical Size and Dimensions Difference Between 24F and 35 Battery
Case Length, Width and Height Comparison
From the table above, the main physical difference is that a Group 24F battery is:
- Roughly 1.2 inches longer than a Group 35
- Similar in width and height (exact height varies slightly by brand)
This extra volume allows more lead and active material inside the case, which is why 24F batteries in the same product line usually offer higher CCA and RC.
Weight and Space in the Battery Tray
The larger case means a Group 24F battery is usually heavier than a comparable Group 35. For most passenger cars this difference is not huge, but it does matter when:
- The battery tray is very close to other components
- The hood clearance is limited
- You are trying to reduce front-axle weight on an off-road vehicle
If your vehicle was originally designed for a 35 battery, the tray and hold-down might not safely accept a 24F without modifications. If it was designed for 24F, installing a smaller 35 battery may leave extra room in the tray, which can be solved with spacers or adapter brackets.
Always check:
- Tray length and width
- Hold-down design and contact surfaces
- Clearance to the hood, coolant hoses and wiring looms
Performance Comparison: CCA, Reserve Capacity and Lifespan
Cold Cranking Amps (CCA) – Cold Starts and High Loads
CCA measures how much current the battery can deliver at -18 °C (0 °F) for 30 seconds while keeping voltage above a specified threshold. Higher CCA means more starting power in cold weather and extra margin for high-compression engines or heavy accessory loads.
Within the same product family, a 24F battery typically has:
- Slightly higher CCA than the 35
- A bit more lead and plate area to support that current
This leads to a common worry:
“If I choose a 24F with much higher CCA, will it damage my starter or alternator?”
The short answer is no. The starter motor draws only what it needs. A higher CCA rating simply means the battery can supply more current if demanded and will hold voltage better in difficult conditions.
Reserve Capacity and Energy for Accessories
Reserve capacity (RC) describes how long a fully charged battery can supply a small load (usually 25 A) before dropping to a specified voltage. In everyday terms, it shows how long you can run lights, audio and other accessories with the engine off.
Because 24F cases are larger, batteries in this group often have higher RC than their Group 35 counterparts from the same brand line. For vehicles with:
- Powerful audio systems
- Winches and off-road lighting
- Frequent key-on, engine-off use
that extra RC can be valuable.
Example Spec Ranges for 24F and 35 in One Product Line
The table below shows typical ranges (not exact specs) you might see in a mainstream battery brand:
| Spec | Group 24F (typical) | Group 35 (typical) |
|---|---|---|
| Capacity (Ah) | 60–70 Ah | 50–60 Ah |
| CCA | 600–800 A | 550–700 A |
| Reserve capacity (RC) | 100–130 min | 90–110 min |
| Weight | 18–23 kg | 16–21 kg |
Always compare the specific models available in your region, as premium AGM/EFB versions may differ significantly.
Does Group Size Affect Battery Life?
Group size itself does not determine lifespan. Battery life is mostly driven by:
- Depth and frequency of discharges
- Operating temperature
- Charging system voltage and regulation
- Vibration and mechanical stress
A carefully maintained Group 35 can outlast an abused Group 24F. When choosing between them, think of group size as a way to get the right physical fit and performance margin, not a guarantee of a certain lifetime.
Fitment and Compatibility: Can a 35 Battery Replace a 24F?
Tray Size, Hold-Downs and Cable Length
Whether you can interchange 24F and 35 batteries safely depends on your vehicle’s hardware:
- Tray size:
- If the tray was designed for 24F, a 35 will physically fit in the length direction, but may leave gaps front or back.
- If the tray was designed for 35, there might not be enough space to install a longer 24F.
- Hold-downs:
- Top-bar clamps may not grab a shorter case securely.
- Side or base-rail clamps must contact the correct surfaces of the case.
- Cable length and routing:
- Short cables designed for a 35 may struggle to reach posts on a longer 24F.
- Cables should not be stretched tight or forced into sharp bends.
A battery that physically “fits” but cannot be secured firmly is a safety risk, especially in an accident or on rough roads.
Terminal Layout and Polarity Considerations
Within each group size, terminal layout is usually standard, but variations exist between brands and regions. When swapping 24F and 35 batteries:
- Make sure the positive terminal remains on the same side as the original battery
- Check that plastic covers, fuses and nearby metal parts clear the terminals properly
- Never cross cables over the battery to “make it reach” – this can stress the wires and increase short-circuit risk
If you are not sure, use a fitment guide or consult a professional mechanic.
Real-World Scenarios from Drivers and Forums
Discussions on automotive forums show some common patterns:
- Owners of SUVs or trucks whose trays easily accommodate a 24F sometimes upgrade from 35 to 24F to gain extra CCA and RC. This usually works well when done with proper hold-down hardware.
- Drivers of compact cars with tight engine bays often stick with Group 35, because trying to fit a 24F requires cutting plastic, moving hoses or risking interference with the hood.
The main takeaway:
24F to 35: usually possible in a 24F tray with spacers or adapter brackets
35 to 24F: only possible if the tray and surroundings provide enough extra length and proper clearance
When in doubt, it is safer to follow the manufacturer’s recommended group size.
Which Is Better for Your Car, 24F or 35 Battery?
Climate and Starting Demands
If you live in a cold climate or frequently start your vehicle with heavy loads running (heaters, blowers, lights), the extra CCA and RC of a good 24F battery can provide useful margin.
In mild climates, a quality Group 35 from a reputable brand will usually crank the engine just as reliably while saving a bit of space and weight.
Vehicle Space and OEM Recommendation
The vehicle manufacturer’s recommendation should always be your starting point:
- If your owner’s manual specifies only Group 35, you should think carefully before trying a larger group.
- If it lists both 24F and 35 as acceptable options, you can choose based on climate, electrical load and budget.
Some aftermarket trays and off-road builds are intentionally sized for either group, giving you freedom to choose.
Driving Style, Accessories and Budget
Ask yourself:
- Do you run powerful audio, extra lighting, a winch or other accessories?
- Do you often sit with the engine off but ignition on?
- How long do you plan to keep the vehicle?
If you have high electrical loads and plan to keep the car for many years, investing in the larger 24F can be worthwhile. If your loads are modest and your driving is mostly short urban trips, a good Group 35 with a strong warranty is often the better value.
A Simple Decision Path
- Tray only fits Group 35: → Stay with 35.
- Tray fits both, mild climate, normal loads: → Either works; choose by price and warranty.
- Tray fits both, cold climate or heavy loads: → Prefer 24F for extra CCA and RC.
- Unsure about clearance or cable length: → Follow OEM group size and consult a professional.
Common Questions About Using the Wrong Size or Higher CCA
Will a Higher CCA Battery Damage My Car?
No. The starter motor and electrical system draw only the current they need. A higher-CCA battery simply has more available current and maintains voltage better during cranking. It does not push extra current into the starter or alternator.
What Happens If I Use the Wrong Group Size Battery?
If the wrong group size physically fits and is clamped securely, the main risk is losing performance margin:
- A too-small battery may have insufficient CCA or RC, leading to hard starts and shorter life.
- A battery that does not fit the tray properly can shift, damage cables or cause short circuits in a crash.
Always ensure correct fitment and secure mounting, not just the voltage and group number.
Does Battery Size Really Matter If Voltage Is the Same?
Yes. Two 12-volt batteries with different group sizes can have very different:
- Cranking performance
- Reserve capacity
- Heat tolerance and life span under heavy loads
Voltage must match, but capacity and current rating must also be adequate for your vehicle.
Can a Battery Be “Too Strong” for My Alternator?
Within normal automotive sizes like 24F and 35, a higher capacity or CCA does not harm the alternator. The alternator’s job is to maintain system voltage and recharge the battery; it regulates its own output. Problems arise when:
- The battery is severely sulphated or shorted
- The alternator’s voltage regulation fails
Choosing a robust, properly sized battery actually reduces stress by keeping voltage more stable.
Starter Battery vs Traction Pack: When Group Size No Longer Matters
Why 24F and 35 Batteries Are Designed for Starting Engines
Both 24F and 35 batteries are primarily starter batteries. They are built to:
- Deliver short bursts of high current for engine cranking
- Operate with shallow discharges and immediate recharge
- Provide adequate performance for the typical life of a gasoline or diesel vehicle
They are not optimised for thousands of deep cycles or for driving an electric motor continuously.
When You Need a Traction or Deep-Cycle LiFePO4 Pack Instead
If your project involves:
- Electric scooters, motorcycles or e-bikes
- E-rickshaws and three-wheelers
- Low-speed electric vehicles and utility carts
- Delivery trikes or other light commercial EVs
then you need a traction battery system, not just a larger starter battery.
A traction or motive-power LiFePO4 pack is designed for:
- Continuous discharge at moderate to high current
- Thousands of cycles at 60–80% depth of discharge
- Integration with motor controllers, regenerative braking and smart chargers
In these applications, group sizes such as 24F or 35 stop being meaningful. Instead, you design around system voltage (48/60/72 V), capacity (kWh) and mechanical integration of the pack.
About Saftec: LiFePO4 Energy Storage and EV Power Battery Manufacturer
Saftec as a LiFePO4 Storage and Traction Battery Producer
Saftec is a LiFePO4 energy storage and power battery manufacturer, focused on:
- Residential and commercial energy storage systems
- Rack-mount and cabinet batteries for telecom and backup power
- Traction batteries for electric two-wheelers, three-wheelers and low-speed four-wheel EVs
Instead of selling universal drop-in starter batteries, we work with vehicle makers and system integrators to build battery packs around the application, ensuring the right voltage, capacity and durability.
OEM and ODM Services for Vehicle and Energy Partners
For OEM and project customers, Saftec offers OEM / ODM services, including:
- Pack design based on your mechanical space and range requirements
- Cell selection, module layout and BMS configuration
- Custom housings with appropriate IP rating and mounting points
- Integration support for CAN / RS485 communication with motor controllers and EMS
Whether you are designing a new EV platform or upgrading an existing fleet to LiFePO4, our engineering team can help define a safe, efficient battery system.
Distributor and Dealer Opportunities
We also welcome:
- Regional distributors for LiFePO4 storage and traction batteries
- EV manufacturers and retrofit shops looking for stable pack supply
- Energy solution providers seeking reliable storage modules
Partners receive product training, technical documentation and after-sales support to help them succeed in local markets.
If your current question is “24F vs 35 starter battery for my gasoline car”, your best option is still to follow the vehicle manufacturer’s recommendation and work with a local auto parts store.
But if you are planning or running electric drive systems or LiFePO4 energy storage projects, Saftec is ready to discuss custom traction packs and storage solutions tailored to your needs.
FAQs: 24F vs 35 Battery for Everyday Drivers
Q1. What is the main difference between a 24F and a 35 battery?
A 24F battery is generally larger, heavier and offers higher CCA and reserve capacity than a 35 battery in the same product family. The 35 is more compact and lighter, designed to fit smaller engine compartments while still meeting OEM requirements.
Q2. Can a Group 35 battery safely replace a Group 24F battery?
Sometimes. If your battery tray, hold-down and cable lengths allow a shorter case and the terminals line up correctly, a 35 can replace a 24F. However, you may lose some CCA and RC, and the battery must still be secured firmly with spacers or adapters.
Q3. Which lasts longer, 24F or 35 battery, if they are from the same brand?
Group size alone does not decide life. Lifespan depends more on how the battery is used, charged and stored. In heavy-duty use, a 24F’s extra capacity can reduce stress and potentially extend life, but good maintenance and a healthy charging system are more important.
Q4. Will using a higher CCA 24F or 35 battery harm my alternator or starter?
No. A higher CCA rating does not push extra current into your starter or alternator; it just gives more reserve capability. As long as the battery voltage and group size are appropriate and the battery is properly installed, higher CCA is generally beneficial.
Q5. When should I move from a starter battery to a LiFePO4 traction battery pack?
If you are only starting a combustion engine, you should stay with the recommended starter battery group size. If you are driving an electric motor for transport or powering heavy loads for long periods every day, you should consider a LiFePO4 traction battery pack designed for continuous discharge and long cycle life—exactly the type of solution Saftec provides for e-mobility and storage projects.
