Battery Capacity Explained: Your No-Nonsense Guide to kWh, Ah, Wh and mAh
If you have ever looked at a battery label and wondered what Ah, Wh, mAh or kWh actually mean, you are not alone. Understanding battery capacity is the key to choosing the right energy storage solution, whether for a caravan, portable power station or home solar battery. In this guide, we explain what battery capacity means, how the different units work, and how to compare batteries with confidence.
The Key Battery Capacity Units You Will See
Different devices use different units. Once you know what each one means, you can translate between them without breaking a sweat.
Ampere Hour (Ah)
An ampere hour (Ah) is a measure of electrical charge. If a battery is rated at 1 Ah, it can theoretically deliver 1 amp of current for one hour. You will spot Ah on deep cycle batteries designed for marine, 4WD, and off-grid solar. A 100Ah lithium battery is a popular choice for many Aussie travellers. But keep this in mind: Ah only tells half the story. It does not reveal the total energy stored unless you also know the voltage.
Milliampere Hour (mAh)
Your phone, tablet, and portable power bank use milliampere hours. It is just a smaller version: 1 Ah equals 1000 mAh. A smartphone with a 5000 mAh battery holds a 5 Ah charge. While mAh is handy for comparing small USB gadgets, it becomes misleading when you move to larger systems. Without voltage, two batteries with the same mAh rating can store wildly different amounts of energy.
Watt Hour (Wh)
This is the unit that makes fair comparisons possible. A watt-hour (Wh) tells you the actual energy a battery stores because it combines charge capacity and voltage. The formula you will use over and over is:
Wh = Ah × V
For example, a 12V 100Ah battery stores 1200 Wh, which you can also call 1.2 kWh. When you compare batteries using Wh, you are comparing apples to apples, no matter the system voltage. If you only look at Ah or mAh, you can easily be misled.
Kilowatt Hour (kWh)
You already see kWh on your electricity bill every quarter. One kWh equals 1000 Wh. A typical Australian household might chew through 15 to 25 kWh per day, depending on the season and whether you run air conditioning in a Brisbane summer or heating in a Hobart winter. Many home battery systems on the market store around 13.5 kWh, and this unit also helps you understand how a portable power station could offset your grid usage during peak times.
Quick Conversion Guide: mAh, Ah, Wh and kWh
Being able to switch between units puts you ahead of most buyers. Here are the core formulas you need, kept in a simple table.
Conversion | Formula | Worked Example |
mAh to Ah | Ah = mAh ÷ 1000 | 20,000 mAh = 20 Ah |
Ah to Wh | Wh = Ah × V | 20 Ah × 5 V = 100 Wh |
Wh to kWh | kWh = Wh ÷ 1000 | 1200 Wh = 1.2 kWh |
kWh to Wh | Wh = kWh × 1000 | 1.5 kWh = 1500 Wh |
To calculate kWh usage, multiply an appliance's power rating (W) by the number of hours it runs, then divide by 1000. For example, a 1000W heater running for 3 hours uses 3 kWh of electricity. If you ever need to quickly work out how much a USB battery pack holds in watt-hours, a reliable mAh to wh conversion always starts by checking the nominal voltage. A power bank rated at 20,000 mAh at 3.7V delivers 74 Wh, while that same 20,000 mAh at 5V gives you 100 Wh.
Real World Battery Capacity Examples in Australia
Smartphones, Power Banks and Laptops
Your current phone likely packs a 4000 to 5000 mAh battery. Because the internal lithium cell operates at around 3.7V, the actual energy content is between 15 and 18 Wh. A slim 65Wh laptop battery can be compared directly against that 100Wh power bank limit. Seeing everything in Wh immediately tells you how many full charges you can squeeze out.
Camping, 4WD and Caravan Batteries
Imagine you are setting up a dual battery system for a trip to the Cape. You buy a 100Ah lithium deep cycle battery with a nominal voltage of 12.8V. Its total battery capacity in watt-hours is 1280 Wh. If your 40W fridge runs about 8 hours a day, that setup can keep your food cold for several days before needing a recharge. Thinking in Wh lets you total up every load, from your LED camp lights to your water pump, so you know exactly what you need.
Portable Power Stations and Home Backup
This is where you will really appreciate understanding battery capacity. Instead of building a piecemeal 12V system, many Aussies are turning to an all-in-one portable power station. These units package a lithium battery, inverter, and outlets into a grab-and-go box that you can use at the campsite, on the worksite, or even plugged in at home during a blackout.
Take the EcoFlow DELTA 3 Plus Portable Power Station as a practical example. Despite its compact body, it boasts a considerable capacity, making it convenient to move around and charge flexibly. It houses a LiFePO4 battery, which is enough to run a refrigerator, charge several devices, and power a few LED lights for a family.
If you demand more and reliable capacity, the EcoFlow DELTA 3 Max Plus Portable Power Station starts at a larger capacity and can be expanded with extra batteries. That level of battery capacity can run a kettle and a microwave in your home. Its extremely fast charging speed ensures it is ready to power the home at any time.
Factors That Affect Real Battery Capacity
Rated capacity is a useful starting point, but the real world always has something to say. These factors can shrink the energy you actually get.
Discharge speed: Drawing a high current can reduce the available capacity of lead-acid batteries due to the Peukert effect. While LiFePO4 batteries are much less affected, heavy loads can still reduce overall runtime. This matters if you plan to run a big inverter load.
Temperature: Extreme Aussie heat, particularly if you leave a battery in a closed vehicle or an unshaded campsite in the Pilbara, degrades performance and shortens lifespan. Lithium iron phosphate (LiFePO4) handles this far better than old-school lead acid, but it is still worth protecting your investment.
Age and cycle life: Every battery loses capacity over time. A quality LiFePO4 battery might still retain 80% of its original battery capacity after 3500 full cycles, while an AGM battery will fade much faster.
Depth of discharge (DoD): You cannot always drain a battery completely without causing damage. Many lithium batteries safely give you 90–100% of their rated capacity, whereas a lead acid battery should ideally stay above 50% DoD to survive.
How to Check and Maintain Your Battery Capacity
Staying on top of battery health means you are never caught off guard.
Phones and laptops: Use the built-in tool. On an iPhone, head to Settings > Battery > Battery Health. Windows users can generate a detailed battery report through the command prompt. These tools show your current full charge capacity compared to when the device was new.
Deep cycle and portable power station batteries: A shunt-based battery monitor, like those from Victron, gives you a live readout of state of charge and amp hours consumed. Most portable power stations display the remaining percentage and estimated runtime right on the screen.
Do a manual check: Occasionally run a known wattage load and time how long the battery lasts until it hits its safe cut-off voltage. Always follow the manufacturer’s safety guidelines if you try this.
Extend the lifespan: Avoid storing batteries in a fully discharged state. Keep them out of direct sunlight, especially during the fierce Australian summer. A shaded, well-ventilated spot does wonders.
Conclusion
Battery capacity stops being confusing the moment you understand how to calculate kWh usage and think in watt-hours and kilowatt-hours. By looking past Ah and mAh and focusing on Wh, you can fairly compare any battery, from the one in your phone to a portable power station that provides backup power for essential household appliances. Next time you are weighing up options, remember to check the Wh or kWh rating, calculate your daily kWh usage honestly, and choose a capacity that fits your current lifestyle. With a solid handle on battery capacity, you will have the confidence to explore further and live more comfortably, no matter where you are in Australia.
FAQs
What does 85% battery capacity mean?
85% battery capacity means the battery can still store about 85% of the energy it could hold when it was new. For example, if a battery was originally rated at 10 kWh, an 85% capacity level means it can now store around 8.5 kWh. This gradual reduction is a normal part of battery ageing and occurs over years of charging and discharging cycles. Many battery warranties in Australia use a remaining capacity percentage, such as 70% or 80%, to indicate expected performance at the end of the warranty period.
How do I check my battery capacity?
On a smartphone, use the built-in battery health section in your settings. For a deep-cycle battery, a battery monitor with a shunt tracks amp hours in and out and shows the state of charge. Many portable power stations also display the remaining capacity as a percentage directly on their screen.
What is the difference between nominal capacity and usable capacity?
Nominal capacity is the rated amount of energy a battery is designed to store under specified test conditions. Usable capacity is what you can actually draw without shortening the battery's life, limited by the recommended depth of discharge. For instance, a 10 kWh solar battery with a 90% DoD gives you only 9 kWh of usable energy, which is a critical detail when sizing a system.