Alright, let’s be honest, energy stuff can get pretty confusing. Watts, joules, watt-hours, and amp-hours... It’s like a whole new language. But if you’re messing around with batteries, portable power stations, or just trying to keep your gadgets alive while camping off-grid, getting your head around this can really help. So, let’s break it all down in plain English, no physics degree required. By the end of this, you’ll know what the heck joules and watts are, how they’re different, and why it matters when you’re choosing stuff like a portable power station for your next big road trip or your emergency backup system.
What Are Joules?
Let’s kick off with joules. Fancy name, simple idea. A joule is the basic unit of energy, which can be scaled up to the watt-hour for practical comparison. Think of it like the total amount of energy stored up, ready to be used. One joule is the energy it takes to move something with a little bit of force over a small distance. But don’t worry about the technical stuff.
Here’s the kind of stuff that makes more sense:
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Picking up a small apple and lifting it one meter? That takes about one joule of energy.
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Your phone battery? That thing stores thousands of joules, because you need loads more energy to keep it running for hours.
Joules are a bit like the “fuel” in the tank or how much energy you’ve got stored up.
What Are Watts?
Now, watts. These guys are all about power, which is how fast you’re using energy. So if joules are how much energy you have, watts are how quickly you’re burning through it.
Here’s the deal: 1 watt = 1 joule per second.
Joules measure the amount of energy stored, while watts measure how quickly you’re using or transferring that energy. For instance, compare joules to water in a bucket and watts to the flow rate from a faucet.
Some examples to make it click:
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A 60-watt light bulb uses 60 joules of energy every second.
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A laptop running at 100 watts is burning through energy ten times faster than your phone charging at 10 watts.
So, more watts = faster energy use. Simple as that.
How to Convert Between Them
If you’re the kind of person who likes a bit of math, here’s how you switch from joules to watts:
Power (W) = Energy (J) ÷ Time (seconds)
Say a gadget uses 600 joules over 10 seconds. Divide 600 by 10, and there you have it: you’re using 60 watts. For more examples, check out the conversion table below:
| Energy (Joules) | Time (Seconds) | Power (Watts) |
| 10 J | 1 sec | 10 W |
| 10 J | 5 sec | 2 W |
| 10 J | 10 sec | 1 W |
| 100 J | 2 sec | 50 W |
| 100 J | 10 sec | 10 W |
| 500 J | 5 sec | 100 W |
| 500 J | 50 sec | 10 W |
| 1000 J | 10 sec | 100 W |
| 1000 J | 100 sec | 10 W |
| 3600 J | 3600 sec (1 hr) | 1 W |
Watts and Watt-hours are Better than Joules
Technically, batteries and portable power units could be measured in joules since joules are the official unit of energy. But here’s the thing: Joules are kind of clunky for everyday use when it comes to these systems. They’re just not super intuitive for showing how long your device will run. It’s a bit like measuring the size of your coffee cup in teaspoons - accurate, but not exactly helpful when you’re half-awake and just want caffeine.
That’s why we typically use watts and watt-hours (Wh) instead. Watt-hours give you a clearer picture of how long a battery or portable power unit can power something, which is way more practical. It rolls the speed of energy use (watts) and the time (hours) into one easy number. For example, a 500Wh battery can power a 100W device for 5 hours. Try doing that math with joules and seconds, and suddenly your morning coffee is cold.
Each watt-hour is equal to 3,600 joules (because 1 watt = 1 joule/second × 3,600 seconds/hour). For example, BLUETTI AC70 power station stores 2,764,800 joules of energy, but more accurately has 768 watt-hours of capacity. That's why we use watt-hours instead of joules - to keep the comparison practical while understanding the physics behind it.
So yes, batteries and portable power units store energy in joules, but watt-hours just make more sense when you’re buying or using them. It’s all about making things easier to understand in the real world.
Watt-hours vs. Amp-hours
But hold on, what about amp-hours, I hear you ask?
On somewhat of a side note (although not really because it’s all connected), this section hopes to explain the purpose of the amp-hour, and why you’ll hear this term along with volt and amperes, too. But don’t worry, with a simple conversion, amp-hours can easily be turned into the now familiar, watt-hour.
An amp-hour (Ah) is a measure of electric charge, not energy. Batteries are often rated by their Ah, and it tells you how much current (amps) a battery can supply over a period of time, specifically one hour.
So if you’ve got a 100Ah battery, that means it could, in theory:
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Deliver 100 amps for 1 hour, or
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10 amps for 10 hours, or
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1 amp for 100 hours
But notice, it doesn’t say how much energy the battery holds. That’s where it gets a little incomplete.
Amps and watts get thrown around a lot, sometimes like they’re interchangeable… But they’re not the same thing. Let’s break it down in plain terms:
As we’ve established, a watt (W) measures how much power something is using. It’s kind of like the total "work" being done. An ampere (amp or A) measures how much electric current is flowing. Think of it like the volume of electricity moving through a wire.
So, how are they connected?
Watts = Volts × Amps
That’s the link. If you know the voltage and the current, you can figure out the power. Let’s say you’ve got a 12V system in your campervan, and your light draws 2 amps. Using the formula:
Watts = 12V × 2A = 24W
So that light uses 24 watts of power. Now, if someone just told you, “It’s a 24-watt light,” you could figure out the amps by flipping the formula:
Amps = Watts ÷ Volts → 24W ÷ 12V = 2A
But why are both numbers used? Well, watts tell you how much power the thing is using in total. It’s great for comparing things like energy use and battery drain. Amps tell you how much current is flowing, which is useful when sizing wires, fuses, and circuit breakers (because too many amps can overheat a wire).
Imagine electricity like water in a hose:
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Amps = how much water is flowing
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Volts = how much pressure is pushing it
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Watts = how hard the water is hitting the wheel at the end (aka the work being done)
Why Are Batteries Measured in Amp-Hours Instead of Watt-Hours?
It usually comes down to what kind of battery it is and who’s using it. Amp-hours are super common in 12V batteries (like the ones used in cars, RVs, and boats), mainly because people in those spaces are used to thinking in volts and amps. It seems a bit backward at first, especially since watt-hours tell you how much energy you’ve actually got, which sounds way more useful, right?
But here's why 12V leisure batteries (and other deep-cycle batteries) are usually rated in amp-hours (Ah) instead of watt-hours. In the world of automotive and RVs, people have been working with amps and volts for decades. Most of the systems run off 12V DC, and installers are used to thinking in amps. So when someone says, “I’ve got a 100Ah battery,” an old-school vanlifer or electrician instantly knows what kind of current that battery can deliver and for how long. It's just the industry shorthand. If everything in your van runs on 12 volts, then using amp-hours is actually pretty straightforward. A 1 amp light will run for 100 hours on a 100Ah battery, and a 10 amp fridge? About 10 hours.
No need to convert to watts unless you’re dealing with inverters or AC appliances that use a different voltage. Furthermore, you can always turn amp-hours into watt-hours:
Wh = Ah × V
So that same 100Ah 12V battery? That’s 1,200Wh of energy. Easy math, but most manufacturers don’t do the conversion because people in that space are already trained to think in Ah. However, a 100Ah 24V battery = 100 × 24 = 2,400Wh. Same amp-hours, totally different energy capacity.
If you're comparing a 12V leisure battery to a portable power station (which always lists Wh), it’s easy to get confused. They’re both storing energy, just labeled differently. And that’s when Ah feels a bit outdated, especially as more people are using a mix of DC and AC gear, solar panels, and inverters.
Why Are Power Units Measured in Watt-Hours Instead of Amp-Hours?
Portable power units usually list their capacity in watt-hours (Wh) instead of amp-hours (Ah) because watt-hours give you a much clearer idea of how much actual energy the unit holds, regardless of voltage. Watt-hours cut through the confusion by showing the total energy in one simple number. Since portable power stations often have different voltages running inside and output options like 12V DC, 110V AC, or USB ports, watt-hours make it easier to compare one model to another and figure out what you’re really getting.
Why This Stuff Actually Matters
So, what’s the point of knowing all this? Well, when you’re looking at portable power stations or thinking about solar panels, it really helps to understand what you’re getting. Here’s what you’ll see on most gear:
Watt-hours (Wh): This tells you how much total energy a power station can store. It’s kind of like the size of your fuel tank. For example, a 500Wh battery can dish out 100 watts of power for 5 hours.
Watts (W): This is the speed limit. It’s how fast your power station can deliver energy. If you try to plug in something that needs more watts than your power station can handle, it either won’t work, or you might break something. Not ideal.
Why power delivery (wattage) is more important than capacity (watt-hours): It's not just the battery life that matters, but also whether your station can support the total power of all connected devices. For example, BLUETTI's Apex 300 delivers 3,840 watts of power, which is perfect for running high-powered devices like refrigerators or power tools, while the smaller AC70 delivers a maximum of 1000 watts of power, which is better suited for lighting, phones, and laptops. Furthermore, it’s not just about the high-powered devices either; what if you want to power several low-powered devices at the same time? You’re going to need the BLUETTI Apex 300.
Using This Information in Real Life
Anyway, here’s how it plays out when you’re out camping or the power’s gone out:
Example 1: You’ve got a 500Wh power station, and you want to run a 60-watt light. Divide 500 by 60. That’s roughly 8.3 hours of light.
Example 2: Want to power a few gadgets at once? Add up all their watt ratings. If the total is less than your station’s max power output, you’re good. If it’s too much, you’ll need to run them one at a time or get a beefier setup.
BLUETTI Portable Power Stations
If you’re in the market for a portable power station, here are a couple that might be worth a look.
First up is the AC70 Portable Power Station. It’s got a 768Wh capacity, which means it can run a 60W light for around 12 hours. But it’s more than just a number on a label. It’s compact, easy to lug around, and can handle small appliances, phones, laptops, and more. You can even pair it with solar panels for a super flexible off-grid setup. Great if you’re the type who wants to be prepared without hauling around a full-blown generator.
Then there’s the Elite 200 V2, which is a smaller, more budget-friendly option. It doesn’t pack quite as much juice as the AC70, but for casual use like charging phones, running fans, or keeping your tablet alive during a power cut, it’s a solid pick. It’s lightweight, easy to stash in a van or car boot, and gets the job done without overcomplicating things.
Where It All Comes in Handy
Think about when the lights go out, or you’re off the grid: you can plan exactly how long your fridge, heater, or fan will run, and if you’re using solar panels, you can figure out how many you’ll need to top up your power station by the end of the day. It’s not just numbers; it’s about knowing what you can rely on when you need power most.
To Conclude
Alright, so here’s the takeaway:
Joules = how much energy you’ve got.
Watts = how fast you’re using it.
Understanding these two can make a big difference when you’re figuring out how to stay powered up, but I think we can all agree that Watts and Watt Hours are by far the most practical numbers to use. So next time you’re checking out a new portable power station, looking at solar setups, or just trying to figure out how long your stuff will last, you’ll know exactly what to look for. The more you understand energy, the more prepared you’ll be, whether you’re camping in the wild or just keeping your phone charged during a blackout.
