Electric vehicles are becoming more common across Australia. If you’re like many who are thinking about making the switch, it’s natural to want to charge your electric car at home using solar energy. But choosing the right home battery for EV charging can be tricky.
A typical solar home battery might store around 10 kWh. Meanwhile, most EVs on the Australian market carry batteries ranging from 50 kWh to 100 kWh or more. That mismatch leads homeowners to a practical question: What size home battery do I need for EV charging?
The answer isn’t simply “add your EV to your household total.” Two things get overlooked in most sizing advice: how much energy you actually pull from the battery after sunset, and whether your battery can deliver power fast enough to run a car charger and your home at the same time. This article covers both.
How Much Battery Do You Need to Charge an EV?
Understanding battery size starts with recognising the mismatch between home storage and EV demand.
The Mismatch
Most standard solar batteries are designed for general household use, not full EV charging. If you rely on an undersized system, it won’t be able to top up your car as much as you’d like. On the other hand, oversizing your system can lead to unnecessary upfront costs.
What Happens in Real Life
In a typical setup, using your home battery for EV charging can quickly drain stored energy. Once the battery is depleted, your EV charging stops or slows, your home loses backup power, and you end up relying more on the grid.
This is why many homeowners find their battery storage for EV charging doesn’t perform as expected. It’s simply not sized correctly, in capacity, power output, or both.
Important Considerations
Frequent deep discharge (draining your battery fully) can also impact lifespan over time, particularly with NMC (nickel manganese cobalt) battery chemistries. LiFePO4 batteries, which are increasingly common in Australian home storage systems, are more tolerant of deep cycling.
Still, balancing discharge depth is a good practice. The goal is to find the right balance:
- Too small → can't support your EV + evening needs
- Too large → higher cost than necessary
- Right size → matches your real overnight demand without compromise
The Number Most Sizing Guides Forget: Power (kW)
Battery capacity (kWh) tells you how much energy is stored. It says nothing about how fast the battery can deliver it. That figure is the rated power output, or maximum discharge rate, measured in kilowatts (kW), and for EV charging, it matters just as much as capacity.
Here’s the problem. Many popular home batteries deliver around 5 kW of continuous power. A 13.5 kWh Tesla Powerwall, for example, is often cited as outputting about 5 kW continuously. Meanwhile, the standard home EV charger in Australia is a 7 kW single-phase wall charger.
A 7 kW charger on its own already exceeds what a typical 5 kW battery can supply. Add your evening household loads (lights, cooking, heating, or cooling) on top, and the battery physically can’t cover both. The shortfall gets pulled from the grid, even if the battery still has plenty of stored energy left.
So, when sizing a battery for EV charging, ask two questions, not one:
- Capacity (kWh): Does it store enough energy for my overnight loads plus EV charging?
- Power (kW): Can it discharge fast enough to run the EV charger and my home at the same time?
What If My Battery’s Power Output Is Below 7 kW?
That’s the common case, and it’s usually fine. You have three ways to work within the limit:
- Charge overnight, when household demand is lowest and the battery has the most spare power to give the car.
- Use a smart charger (or energy management system) that throttles EV charging to whatever the battery can spare at the time.
- Choose a higher-output battery, or stack modules, if you regularly need to run the charger and heavy household loads at once.
A slower overnight charge is often all you need anyway. A 7 kW charger adds roughly 40–45 km of range per hour, so even a few hours covers the average day’s driving.
Key Factors That Determine Solar Battery Size for EV Charging
Choosing the right solar battery size for home use involves more than just looking at your EV. Several factors come into play:
1. EV Battery Capacity
Most EVs sold in Australia today fall between 50 kWh and 100 kWh+. Popular models like the Tesla Model Y (60 kWh), BYD Atto 3 (60.5 kWh), and larger SUVs well above 80 kWh reflect how the market has shifted. The larger the battery, the more energy needed for a full charge, though in daily use you’re usually topping up, not filling from empty.
2. Daily Energy Consumption (Driving)
How much you drive daily directly affects how much energy you need. In Australia, the average EV consumes approximately 15–18 kWh per 100 km, depending on size, driving style, and conditions.
Here’s what that looks like in practice:
| Daily Driving Distance | Estimated Daily EV Energy Use (at ~16 kWh/100 km) |
|---|---|
| 20–30 km/day | ~3–5 kWh |
| 40–60 km/day | ~6–10 kWh |
| 80–100 km/day | ~13–18 kWh |
For context: According to ABS data, the average Australian drives approximately 33 km per day (about 12,100 km per year). RACV figures put it around 36.4 km per day. This means most Australian drivers fall into the light-to-moderate range, needing roughly 5–7 kWh per day just for their EV.
This is one of the most important inputs when deciding how to size a home battery.
3. Charging Frequency
Do you charge daily, or only a few times a week? Your EV charging battery setup should match your charging habits.
- Daily charging → smaller, consistent energy draw from your battery each night
- Occasional charging → higher demand per session, requiring more stored energy at once
4. Evening Household Energy Usage
Your battery doesn’t just power your EV. It also supports your home in the evening, and this is where most sizing goes wrong. The common mistake is adding your entire daily household consumption (often quoted at 15–20 kWh) to your EV’s daily use and buying a battery for the sum. That overstates what you need for two reasons:
- Daytime load is mostly covered by solar directly. While the sun is up, your panels run the house and charge the battery with the surplus. The battery only has to carry the load after the panels stop producing. The number that matters is your evening/overnight consumption.
- Round-trip losses are real but small. Energy in doesn’t all come back out. For lithium batteries, this loss is typically about 10% of the stored energy, so built in a modest buffer rather than sizing to the exact kWh you expect to draw.
Size for your evening and overnight loads plus overnight EV charging, then add a small margin for losses and cloudy stretches.
5. Future Expansion
Planning ahead is crucial. A scalable EV solar battery setup ensures your system remains useful over time. Consider whether you might be adding another EV, installing high-energy appliances such as a pool heater or ducted air conditioning, or increasing overall household energy use.
6. Solar System Size
Your solar panels determine how much energy you can generate daily. As a general guide, a 6.6 kW solar system in most parts of Australia generates around 25–30 kWh per day on average, while a 10 kW system may generate 38–45 kWh per day.
A larger solar system is ideal if you want your solar battery to charge EV more efficiently, reducing reliance on the grid.
What Size Home Battery Do You Need for EV Charging?
Here’s a practical guide to help determine the right home battery for EV charging based on combined evening and EV usage.
How to read these numbers: The recommendations below combine your evening/overnight household load plus overnight EV charging, with a small buffer for round-trip losses, not your full daily household consumption. Alongside capacity, check the battery’s continuous power output (kW) against your EV charger and evening loads.
Small Usage (Short Daily Commute)
- Driving: 20–30 km/day
- EV energy use: ~3–5 kWh/day
- Evening home + EV demand: ~12–17 kWh
- Recommended size: 15–20 kWh battery
This setup supports EV top-ups along with evening household use, with a little headroom for cloudier days.
Moderate Usage (Longer Commute or Regular Driving)
- Driving: 40–60 km/day
- EV energy use: ~6–10 kWh/day
- Evening home + EV demand: ~15–22 kWh
- Recommended size: 20–25 kWh battery
With this level of use, a standard 10 kWh battery drains quickly. A 20–25 kWh system gives a better balance between EV charging and household needs.
Heavy Usage (Frequent Driving)
- Driving: 80–100+ km/day
- EV energy use: ~13–18 kWh/day
- Evening home + EV demand: ~22–30 kWh
- Recommended size: 25–30 kWh battery
At this level, smaller systems become impractical. A larger EV charging battery storage system ensures consistent performance without sacrificing home energy needs.
Future-Proof Home (Multiple EVs or Growing Demand)
- Two EVs or increasing energy demand
- Recommended size: 30 kWh+ battery (and check discharge power, not just capacity)
This level of capacity supports long-term flexibility and reduces the need for future upgrades. With multiple EVs, output power becomes as important as storage, so a higher kW rating or multiple units is often worthwhile.
VoltX Energy Battery Systems
VoltX Energy offers scalable solar battery systems in Australia. They’re designed for modern energy needs, including EV charging. Key advantages include:
- Flexible capacity expansion to grow with your household
- Durable design to withstand harsh Australian weather conditions
- Ideal for solar panels and battery for EV charging setups
- Reliable performance for both home and EV use
This makes VoltX Energy a strong option for homeowners planning to integrate EV charging battery storage into their energy system.
Cost of Charging an EV at Home with a Battery
Understanding the cost to charge electric cars from home helps highlight the value of a properly sized system.
Grid-Only Charging
Charging directly from the grid is the simplest option, but costs can add up. With average Australian prices sitting around 30 cents per kWh, fully charging a 60 kWh EV battery from the grid costs roughly $18. Over a year of average driving (around 12,100 km at 16 kWh/100 km), that's approximately $581 in electricity costs per year, plus more if you're on peak tariffs.
Solar-Only Charging
Using solar panels reduces costs significantly, with the effective cost of solar energy typically sitting between 5 and 8 cents per kWh over the life of the system. However, solar-only charging only works during daylight hours. Without storage, excess energy generated during the day is often exported to the grid at a lower feed-in tariff instead of being used when you need it.
Solar + Battery (Best Outcome)
A solar battery for EV charging allows you to store excess solar energy and use it later, such as overnight charging when electricity rates are highest. This setup offers lower charging costs over time, greater energy independence, and reduced reliance on peak electricity rates.
For a household generating sufficient solar energy, the effective cost per kilometre of EV driving can drop to just a few cents. While there is an upfront investment, the long-term savings and flexibility make better storage for EV charging a practical choice for many Australian households.
Charge Smarter, Not Just Bigger
Choosing the right home battery for EV charging is about matching the system to your lifestyle. EV usage, household energy demand, solar generation, discharge power, and future plans all play a role in determining the ideal system size.
A well-matched setup ensures your EV charging is reliable without sacrificing your home's energy needs. With the right balance, a solar battery backup can be your smart energy solution, delivering real daily value.
Still wondering, “What size home battery do I need for EV charging?” Explore VoltX Energy's battery systems and get expert advice on sizing. Build a system that works today and scales for tomorrow.
Frequently Asked Questions
What size home battery do I need to charge an EV?
It depends on your driving and, importantly, your evening and overnight household energy use, not your whole day (daytime load is largely met by solar directly). Most Australians drive around 33 to 36 km per day, needing roughly 5 to 7 kWh just for the EV. Combined with typical evening household loads and a small buffer for round-trip losses, a battery in the 15 to 30 kWh range suits most homes.
Does my battery's power rating matter, or just its capacity?
Both matter. Capacity (kWh) is how much energy is stored; power output (kW) is how fast it can be delivered. Many home batteries output around 5 kW, yet a standard single-phase EV charger draws about 7 kW, so the charger alone can exceed the battery’s output and force a top-up from the grid even with energy to spare. Charging overnight or using a charger that throttles to available power keeps you within the limit.
How long will a home battery last when charging an EV?
A standard 10 kWh home battery can add roughly 60 km of driving range to an average EV, which may only take an hour or two of charging to deplete. If you're also powering your home from the same battery in the evening, it drains faster. Larger systems (20–30 kWh) last significantly longer and can handle both EV and household loads through the evening.
Is it cheaper to charge an EV with a solar battery?
Yes, substantially. Grid electricity in Australia averages around 30 cents per kWh, while solar energy effectively costs around 5–8 cents per kWh over the life of the system. Storing surplus solar and charging your EV overnight can reduce your per-kilometre driving cost to just a few cents.
Can I charge my EV and power my home at the same time?
Yes, but only if the battery is sized for it in both capacity and power. Evening demand often overlaps with EV charging, and a typical ~5 kW battery can’t always supply a 7 kW charger plus household loads at once, so it draws the difference from the grid. Checking the battery’s continuous power rating, not just its kWh, is what makes simultaneous use work.
Can I add more home battery capacity later?
Many home battery systems, including modular options available in Australia, are designed to be expanded over time. You can start smaller and add capacity as your needs grow, such as when you add a second EV or increase household energy use. Just make sure your initial inverter and wiring are rated to support the additional load, and that added modules lift power output as well as capacity if you need it.
