We all know how much manufacturers lie about battery life. In fact, researchers found that 86 percent of them overstate it, often by testing with unrealistic usage conditions. The marketing numbers are unhelpful because you’d never be using Microsoft Office for 14 hours straight!We can take steps to reduce our battery life usage, but, wouldn’t it be better if we just had the right number to start with?Thankfully, there's one thing they can't lie about: battery specifications. In this guide, we'll help you calculate how long you can actually expect your next laptop to last.

The calculation is quite simple to do. We’ll go into how to find the numbers in a moment, but here’ how we do it:

Find the battery specification in watt-hours (the units are Whr or Wh)

Divide by your expected wattage (in W). A computer under normal use will take 10-15 Watts.

For example, take a laptop with a 100Wh battery such as the newest MacBook Pro. Under normal use, it should last 7-10 hours: 100Wh divided by 15 and 10 Watts gives us 7 to 10 hours respectively.

The result specifies how long your laptop should last, though it may be a tad lower due to a voltage drop-off at the end of a charge. Many laptops are also set with sleep or hibernation modes that kick in when the battery drops below five or ten percent charge to protect data, so keep that in mind too.

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NOTE: Don't be afraid to do some re-arranging. For example, multiply the battery life you want and your estimated wattage and you'll find the watt-hour specification you should look for in your laptop search.

ESTIMATING WATTAGE

Finding your laptop’s wattage is the hardest bit. Here is a few ways we can find or estimate it.

A laptop under full load will use anywhere between 65-90W. For this reason, most gaming laptops under full load can only last about an hour. To find exactly what your full load is, either:

Find the maximum wattage on the product specification page

Check the wattage on the back of your charging power brick (adaptor)

We can also roughly link up activities to the wattage they’ll take:

60-maximum: heavy gaming, video rendering

40-60W: light gaming

30-40W: video or photo editing

20-30W: watching HD video online

15-20W: watching HD video offline or using multiple applications

10-15W: normal use, such as web browsing (with not too many tabs), text editing or playing music

8-10W: minimum wattage with the screen on

There are obviously hundreds of factors that determine your power usage, but we’ll run through a few of them. You should be looking at the upper ranges of the estimates above if you:

Have a habit of leaving applications running in the background

Buy a laptop with a dedicated graphics card (if it says you have Intel graphics, then you don’t have a dedicated one)

Have your screen brightness up high

Plug in other devices, such as phone or headset

Have a screen size above 15 inches

FINDING WATT HOURS

You should be able to find the watt-hour number on any descriptive specification sheet. The numbers are also available from the specifications tab on online stores, third-party reviewers and official store pages such as the Dell web store.

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The number of cells in the battery isn’t helpful to our calculation, so ignore it. If you manage to find mAh and Volts, you can convert that to watt hours with an online calculator.In the minority of cases, you won’t find any of watt you need (get it, watt) and you might have to guess based on laptops of a similar model or price range.You shouldn’t expect a rating to go higher than 100Wh due to lithium-ion flight restrictions. Anything higher needs to be approved by the airline before a flight, so manufacturers aren’t making batteries above that point.

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The LG Gram 15 is a good laptop, for what it is. But what it is is a dinosaur. Most people won’t want or need a $2000 laptop with a 1080p 15.6-inch display in 2018—never mind how light it is or how reasonable the battery life. This might be the laptop for a parent who complains about their reading glasses and uses 40-point font on their Kindle (hi Mom), but for everyone else it’s okay to get something smaller, and just a little heavier. The guts of the LG Gram 15 just aren’t fast enough.

Star Trek II, Mark Ruffalo's Hulk, Ms. Pac-Man. Sometimes the sequel is much better than the original. Let's hope that's the case with "always-connected" laptops, a new generation of Windows 2-in-1s that use Qualcomm Snapdragon processors and built-in 4G to provide the constant connectivity and long battery life you get from a smartphone.

We've tested the first two of these laptops: the $999 HP Envy x2 and the $599 Asus NovaGo TP370QL, and we were impressed with their epic 12 to 15 hours of endurance. Unfortunately, their mix of sluggish performance, compatibility issues and tiny storage drives raise the question: Who are they for?

"Battery life just is not a key driver for consumers," said Stephen Baker, vice president of industry analysis at NPD. "Even on a smartphone, the vast majority of consumer connectivity occurs over Wi-Fi and not over a cellular connection, making the cellular connectivity likely less important to PC buyers."

That kind of gap sounds really scary and makes you question the entire point of this project in the first place. Until you realise that while these Snapdragon-powered Windows PCs can sort of handle your traditional Windows programs, the system is really designed to work best with native UWP (Universal Windows Platform) apps installed from the Microsoft Store.So I ran WebXPRT again in Edge, and the Nova Go’s score doubled from 84 to a 163; still shy of Intel Core m3, but much more acceptable. And in real life, the difference in horsepower is even less of an issue. Sure, you’ll run into the occasional hitch or a bit of input lag, but those are the kinds of things that you see on a lot of budget and mid-range systems. It’s frustrating, but not deal breaking.

And those budget and mid-range systems based on Intel silicon don’t have the promised battery life of a Qualcomm Snapdragon device. In our traditional battery rundown test, where we stream a YouTube video over Wi-Fi until the computer dies, the Nova Go lasted just 13 hours and 49 minutes. I just say because that time only puts the Nova Go battery life 15 minutes ahead of the 13:24 posted by a non-touch XPS 13 with an 8th-gen Core i7 CPU. But when I did the same test in Edge, battery life shot up another hour and a half to 15:16, which is the best battery life we’ve seen on any laptop in the last two years. It’s not quite the 20+ hours Qualcomm is teasing elsewhere, but still pretty great.

The fingerprint reader isn’t really necessary, but it’s a nice bonus.

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But those are just tests design to drain the battery quickly. Oftentimes, in real life, the Nova Go’s longevity is even better. Over the course of a weekend spent testing the system, I was surprised at how many times after 45 minute browsing sessions spent trying to find non-sold out Avengers tickets, looking at stupid memes or whatever other inane shit people use computers for when they aren’t working, the battery percentage dropped just one or two per cent. This thing truly sips juice.

And then there’s the Nova Go’s built-in 4G LTE modem. If you want internet, it’s always available. Just pop-in a SIM from your carrier of choice, add the correct access point (APN) info into Windows and off you go. No longer do you feel like a Wi-Fi addict, hunting for your fix when you’re away from home. You just open the computer and with the Nova Go’s near instant wake times and persistent background connection, you’re always ready to browse. This is kind of the always-connected dream people keep associating with the coming of 5G, and it’s a treat. Though it’s also true that this isn’t even close to the first laptop with 4G LTE, Microsoft even just released a Surface with 4G connectivity earlier this year.

Every laptop should have always-on internet.

Back to the Asus Nova Go. As much as I like it, I’m not sure it’s for me personally. It’s not the computer, it’s me. I need the ability to edit photos or videos on the go, and while the Nova Go can do both of those things, I wouldn’t exactly call it speedy. I’m also worried that with all the various devices that need internet, such as your phone, tablet, even cars, people’s mobile data bills are going to balloon up uncontrollably now that you need to pay for laptop data too. Then there’s its price tag. For $600/£425 you only get 4GB of RAM and 64GB of storage, which seems a bit steep. If Asus were to bump both of those up a bit without increasing the price, than suddenly things could get a lot more interesting.

In a way, the Asus Nova Go is almost an ideal laptop for students. Its fantastic battery life turns forgetting to recharge the system at night from a disaster into an issue you might not even notice. And its built-in modem means the internet is always available and its CPU is more than enough to handle web browsing or working in Google Docs or Office 365. Even the abomination that is Windows 10S—which comes pre-installed by default—isn’t that big of a deal, since you can upgrade to normal Windows 10 whenever you want, for free.

Windows on Snapdragon chips might not be a full on PC revolution, but it’s nice to have more choice when it comes to different chips strengths' and weaknesses. And based on how much effort Qualcomm has invested making Windows work on ARM, this is only the beginning.