Why Laptop Batteries Can’t Get Any Bigger (For Now)

No matter how fast powerful laptops get, and no matter how ridiculously big and beefy a portable gaming rig might be, their batteries are basically stuck at their current size. Why? You can thank the Federal Aviation Administration. 

Lithium-ion batteries are a wonder of convenience. They can power computers for days, they charge quickly, and they don’t suffer from any weird “memory” effects, and lithium is the lightest of metals, which is good for portable devices.

But they’ve got some annoying tendencies. Sometimes they swell. Sometimes they catch fire. Airlines hate it, and so they’ve made rules about how big a battery can be to come with you on a plane. And nobody wants their laptop confiscated at TSA, so electronics manufacturers basically have to comply.

Why Do Lithium-Ion Batteries Catch Fire?

Batteries rely on an ongoing chemical reaction to generate power, called an oxidation-reduction reaction. As a battery ages, this chemical reaction no longer completes perfectly. Sometimes, the imperfect reaction generates gases such as carbon dioxide and carbon monoxide, which can cause batteries to swell. Most lithium-ion batteries inside consumer electronics are made in a roll style, with layers of metal and chemicals separated by plastic. If that plastic degrades or gets damaged, the battery can start to heat up and eventually even catch fire, in a process called “thermal runaway.”

A damaged battery releases heat and gases, which can further break down the battery, damaging more of the protective layers, releasing yet more heat in a chain reaction. At the same time, the heat can vaporize the electrolyte, which can then catch fire. If there is free lithium in the battery, then it can react with water to produce hydrogen, which obviously doesn’t help matters.

Once a swollen or punctured battery has caught fire or exploded, traditional fire extinguishers may not be much help. If you’re prying at a smartphone battery and it catches fire, it’s not too hard to handle usually. You can put it in a bucket of sand or carry it carefully outside to let it burn itself out.

But the bigger the battery, the more serious a fire can be, and the harder it is to put out. Last year, a Tesla’s batteries caught fire on a California freeway, and firefighters had to dump 6,000 gallons of water on it to quench the flames. Tesla itself estimates its batteries take 3,000–8,000 gallons to put out, and the number can go as high as 40,000 gallons, just for the batteries in a car.  Now, imagine something similar happening on a plane, and you can see why airlines are wary of anything containing a big li-ion battery. 

Planes Limit Rechargeable Li-Ion Batteries to 100 Wh

This is why planes have a hard limit—100 watt-hours—on rechargeable li-ion battery capacity, and a maximum of 2 grams of lithium in non-rechargeable batteries. Current FAA regulations allow an individual to carry “up to two spare larger lithium ion batteries (101–160 Wh) or Lithium metal batteries (2-8 grams).” The FAA’s European equivalent, the EASA, also enforces a 100 Wh maximum, with up to 160 Wh allowed with the permission of the airline. Devices can be packed in checked luggage “as long as you take measures to prevent unintentional activation,” says the EASA, but spare batteries and power banks must be carried in the cabin.

Batteries do sometimes catch fire on planes, and airlines are watching these incidents very closely. The FAA’s statistics say that there have been 19 LI battery incidents this year so far, compared to 89 for last year.

And that explains why even the biggest laptops don’t go above 100 Wh for their built-in batteries. If they did, you couldn’t fly with them. That’s fine for smaller laptops. The latest 14-inch M4 MacBook Pro packs a 72.4-Wh lithium-polymer battery, for example. But the 16-inch version is right up at that 100 Wh limit. 

This is why we are so hot on battery safety here at iFixit. Swapping out a dying phone battery is a common repair, so you have to play by the rules. It might seem tempting to forgo the proper disassembly required to get to the battery, and to just lever it out instead, but that can end up triggering an explosive situation. Likewise, you should never use metal implements that could pierce the battery.

What To Do If Your Battery Starts To Swell, Smoke Or Catch Fire

Staying safe depends on how you use batteries. You’re unlikely to have a serious fire if you’re following all the correct instructions for a repair. Discharge your battery as low as possible before starting the repair, to reduce the chance of a reaction getting out of hand. It’s also essential to discharge the battery before changing it, to reduce the amount of energy available if things do go wrong.

When we tried getting batteries to catch fire by stabbing them, we found that the fires were a lot smaller and a lot harder to ignite when we’d drained the battery first.

The easiest way to deal with a single battery fire is to throw it (very carefully) into a containment device. If you buy one commercially, you’ll receive a bag or a box that can withstand very high temperatures, while remaining cool on the outside. It may also come with heat resistant gloves for getting the flaming device into the bag, and water for dousing to mitigate thermal runaway. We like to keep things simple: a metal bucket with a little sand in the bottom is plenty for most battery fires you’re likely to see in a lifetime of electronics repairs.

And manufacturers can design batteries so that they’re a lot less likely to ignite. That’s part of why we applauded the steel-case iPhone 16 Pro battery, which doesn’t have the fancy new electrically released adhesive.

But it’s not always so straightforward. For example, remote control (RC) car and drone racers risk damage every time they crash. And while a laptop will have good charge-management, overcharging can be as hazardous as sticking a screwdriver into the battery. Take a look at this RC car, whose battery was intentionally overcharged. 

If you’re working in an environment where battery fires are more likely—maybe you run a repair shop, or you’re an RC racer, or you operate a passenger airline—then extra precautions are necessary. The FAA’s training video for in-cabin battery fires on planes is also worth a watch for anyone using LI batteries in risky situations.

Shipping Batteries

We’ve seen that li-ion batteries are dangerous if damaged, and why the FAA doesn’t want you stuffing spares into your checked baggage, down in the hold where any fires cannot be spotted, and cannot be fought by the crew. It doesn’t help that hold luggage gets tossed around and abused, unlike your cabin baggage, which you probably won’t attempt to throw down a 20-foot ramp or crush under bigger, heavier cases.

This all explains the rules around shipping batteries. You’ve probably noticed the warning labels on the packaging of any battery-powered gadget you’ve bought in recent memory. These devices can be transported by air, whereas naked batteries, like the spares we sell at iFixit, can only be shipped by surface transport.

Here’s what the US DoT has to say in its Lithium Battery Guide For Shippers: “Unlike standard alkaline batteries, most lithium batteries manufactured today contain a flammable electrolyte and have an incredibly high energy density. They can overheat and ignite under certain conditions, such as a short circuit or improper design or assembly. Once ignited, lithium cell and battery fires can be difficult to extinguish.”

Batteries inside laptops, speakers, and so on are encased, which means that they are much harder to damage. In addition, that “casing,” and the packaging surrounding it, make it harder for thermal runaway to propagate to other batteries or conductive materials. Imagine a cargo plane’s hold stacked with boxes of bare laptop batteries and you can see how wrong things could go.

Lithium-based batteries are incredible, allowing us to use our phones, laptops, and other devices for hours, days, or even weeks away from a power outlet. But as we have seen, they also have downsides. In most cases, these downsides are worth the risk, and in general use, most of us will never have to deal with a raging li-ion battery fire. And knowing these risks (as you now do) reduces them substantially. It might be frustrating for some that laptops cannot pack even more battery power, but on the other hand, now we know the dangers, it’s actually pretty comforting to know that the video editor sitting next to you on the plane doesn’t have a 300 Wh time bomb on their lap, ready to fuel a flight-ending blaze.