When you start shopping for solar batteries or portable power stations, you’re immediately hit with a wall of technical jargon: volts, amps, Amp-hours (Ah), Watt-hours (Wh)… and somehow, you’re just supposed to know what they all mean.
Even outside of the world of solar and backup power, you’ve probably seen power tools and other rechargeable devices with stickers that say stuff like “6Ah” or “9Ah”. Naturally, most people assume, “More amp hours must mean more power!” But that’s not always true.
Today, we’re breaking down some of the most misunderstood terms and specifications in the solar world: Amp-hours vs Watt-hours. We’ll explain what those terms mean, how they’re related, and which number really matters when choosing your next battery or power station.
Amp hours (Ah) are a measure of charge capacity. In plain English, they tell you how much current (in amps) a battery can deliver over a period of one hour.
For example:
That’s why Amp-hours are often compared to the size of a gas tank. The measurement tells you how much charge a battery holds, but not how powerful that energy is when it’s used. Because here’s the catch: amp hours don’t account for voltage, and that’s where things start to get tricky.
Voltage (V) represents the potential energy, or the “pressure” pushing electricity through a circuit. If Amp hours are the metaphorical gas tank, voltage is the octane rating of the fuel.
So, while Amp hours tell you how much current is available, voltage determines how strong that current actually is. Without considering both, Amp hours can be extremely misleading.
That’s why Watt hours (Wh) are the more accurate way to measure energy storage — they combine both current and voltage into one simple value.
If you’re still finding battery voltages confusing, we actually have a guide that breaks it all down: Understanding Solar Battery Voltages.
Now we’re getting to the most important measurement for power stations, solar batteries, and pretty much any other type of backup power storage: Watt-hours. Simply put, Watt hours measure the total stored energy of a battery.
The formula is simple:
Watt hours = Amp hours × Volts
If you double the voltage while keeping amp hours the same, you double the energy.
So, if you only look at Amp hours without voltage, you might think you’re getting a bigger battery than you really are. Unfortunately, a lot of companies know this, which is why you’ll often see “6Ah” in huge bold print on a box, while the voltage sits in fine print somewhere below it.
In other words, they’re playing on the ignorance of uniformed buyers. That’s also the reason why we’re here to break this type of stuff down for you.
Let’s say you’re helping Mr. Health and Safety install a solar kit at his tiny home. You bring your drill, which uses a 20V 4Ah battery, while his uses a 12V 5Ah battery.
At first glance, 5Ah sounds better since it’s a bigger number, but let’s do the math:
So even though the battery pack attached to his drill says “5Ah” and yours says "4Ah", your drill battery actually stores more energy because of the higher voltage.
That’s why comparing amp hours alone can cause confusion and costly mistakes, especially when you’re about to sink thousands of dollars into a high-capacity power station.
Again, the Watt-hour number is where you can plainly see how much power the battery can store, and how much of it will be usable.
Basically, Watt-hours tell you how much energy you’re actually working with, no matter the voltage. It’s the same reason we always try to list Watt-hours whenever we review any type of solar battery or portable power station.
Speaking of solar batteries and power stations, battery capacity confusion happens all the time. Some entry-level 12V batteries, like the Redodo 12V Mini and other cheap LiFePO4 units found on Amazon, advertise big Amp-hour numbers to seem competitive, but when you multiply by their low voltage, they end up storing far less total energy than you’d expect.
That’s why when we review power stations and batteries, from a tiny Anker C300X Portable Power Station to a BigBattery 48V Husky 2 or EG4 WallMount All Weather Battery, we always list both the Amp hours and Watt hours. It’s the only way to make a clear apples-to-apples comparison.
If you want to dive deeper into picking the right battery for your solar setup, check out our article: How to Size a Battery for Your Solar Power System. That guide will walk through how to total up your watts and calculate the watt-hour capacity you’ll actually need.
There are times when looking at Amp hours makes sense. This is mostly when your entire system runs on a single voltage, like a 12V camper or trailer.
For example, let’s say you’ve got a 12V 100Ah battery running a fan that draws 5 amps. All you have to do is divide:
100Ah ÷ 5A = 20 hours of runtime
In this case, knowing your Watt hours isn’t that important because everything runs off 12V. But the moment you start dealing with inverters, higher-voltage batteries, or mixed systems, Watt hours become essential for accurate comparisons.
Most home backup and off-grid solar systems involve mixed voltages. The same is true when you’re running mixed loads off a power station. Your lights, fans, phone, laptop, and appliances might run on 120V AC or 240V AC, while your batteries store power at 12V, 24V, or 48V DC.
Since energy is constantly being converted between different voltages by the inverter, Watt hours will give you a single standard measurement that applies across everything. It lets you see exactly how much energy you’re storing and using, without doing voltage conversions for each component.
So next time you’re comparing solar batteries, don’t get fooled by marketing. Always look for the Watt-hour rating, or check our reviews, as we always list that when we’re breaking down the specifications for any product. That’s the number that actually determines how long your gear will run.
If this stuff interests you, or you just want to get more out of your batteries, we recently put together a how-to guide for extending battery life in power stations and solar batteries. In that guide we also covered the history of battery chemistry and some of the terms we still use today, like “volt”.
To sum it up:
Formula:
Wh = Ah × V
If a power station or solar brand only lists Amp hours, multiply it by the voltage yourself. Don’t let bold numbers trick you into thinking you’re getting more battery than you're actually paying for.
Amp hours are useful, but they don’t tell the whole story. To truly understand how much power storage you’re getting, always convert to Watt-hours. It’s the key to comparing batteries fairly and making smarter buying decisions.
Now you know the difference, so the next time you see “12V 100Ah” on a specifications sheet or label, you’ll know exactly what that means. More importantly, you’ll know whether that battery or power station you're looking at is a good deal or the company is using some clever (deceptive) marketing.
Shop Solar: www.ShopSolar.com/solar-batteries
Signature Solar: www.SignatureSolar.com/batteries
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