iOS Power Best Practices

Before you read, a quick disclaimer: I’m not an electrical engineer, the only expertise in the content below is that I’ve owned iOS devices for the last decade. At some point, I needed to charge them, and these are the methods I’ve used. Your results may vary. While my goal is to outline safe and effective methods for charging, I’m not responsible for your device going into meltdown as a result of something you see here.

Between myself and my wife, I’ve owned every iPhone since the 3G. I’ve also had my hands on nearly every revision of the iPad since it was released. However, I’ve yet to upgrade anyone to the iPhone 8 or the iPhone X in the @vmstan home, so I have no first hand experience with wireless charging.

This is part “best practices” around iOS device charging, and part technical review of a variety of different products from wall outlets and cables to battery packs.

Measuring Power

To restate, I’m not an electrician, but I’ll attempt to outline a few basic power concepts before we proceed. When talking about powering any mobile device, there are four major measurements you should keep in mind.

Three relate to power flow:

  • Amperage (Amps - A)
  • Voltage (Volts - V)
  • Wattage (Watts - W)

One relates to capacity:

  • Milliamp Hours (mAh)


Think about electricity like you think about water. Normally the idea of mixing the two is generally awful, but since you’ve seen how water come out of the tap, and you can’t ‘see’ electricity, it might make it easier to visualize.

Amperage is the volume flowing through the pipe. Visualize that you have 1 liter of water moving through a pipe, and pretend this is 1 amp of electricity.

Voltage is the pressure flowing through the pipe. Take your 1 liter of water; if it has no pressure pushing on it, it'll just sit in the pipe. Similarly if you had 1 amp of power, but no voltage, it won’t move down the line.

If you only have 10 psi of water pressure, your water will move … slowly. If you have 100 psi of water pressure, you might start to damage your pipe if it’s not designed for that much pressure. You want enough to do the job, but not enough that it causes damage.

So amps are the thing you need (the power) and volts are the measurement of fast you can get there.

Wattage is a way to represent the total power delivery. Watts = Volts x Amps


In our phones, and other portable devices, the battery capacity is measured in milliamp hours (mAh) - the higher the mAh, the longer the device can draw power from the battery, and the more Candy you can Crush. Typically the larger the mAh, the larger the battery and the larger the device.

As an example, the iPhone 7 has a battery rated at 1,960 mAh, while the larger iPhone 7 Plus reaches 2,900 mAh.

But you can't always just compare raw mAh from the battery. The iPhone 8 and iPhone 8 Plus actually have smaller batteries than the 7-series, but have the same or better life, due to more efficient processors that draw less power.

Apple doesn’t really advertise these numbers, they come normally from mandated filings, or from people who do a teardown of the device and decipher the details within. Apple is happy to tell you that an iPhone X gets two more hours of usage than an iPhone 7, but not that the X has an 2,716 mAh battery.

Still, it's helpful to have a rough idea of the capacity of your device. Generally speaking, the larger the battery, the longer it'll stay charged and as a result, the longer it'll take to charge.

Apple Charging Options

Stock iPhone charger

Everyone who has owned an iPhone knows they come with a Lego sized power brick and a Lightning cable. Carry this combination around with you and you’re set to charge your phone anywhere you and can find a power outlet. If you saved every charger from every iPhone you ever owned you’d have a little collection you could spread around your house. These chargers are essentially unchanged from what shipped with the the original iPhone.

The stock charger is small, and has one purpose, to take the raw power coming off the grid, into your home, and turn it into something the iPhone can consume. Given the size, it’s actually an amazing piece of engineering in itself. There are numerous teardown available for this charger online, but this one from Ken Shirriff is one of my favorites.

Even without a tear down, you can take your charger and read the details on the backside, and in doing so you’ll get a couple of important details:

  • Output 5V, 1A

Remember what we said before. Volt (V) is the pressure of the electricity coming down the line. Amp (A) is the amount of it. If you multiply 5 by 1, you get 5. This is the number of Watts (W), hence why even though it doesn't show it on the device, the stock charger is advertised as the Apple 5W USB Power Adapter.

Up until the iPhone 5, this 5W limit was as much power as the iPhone could handle coming in at any one time. Using a larger charger would not (generally) damage the device, it just wouldn’t draw anything more than the 5W rating. Starting with the iPhone 5, Apple gave the iPhone the ability to use a more robust charger, and would result in faster charging.

Stock iPad charger

The iPad ships with either a 10W or a 12W (depending on model) charger. If you read the details on the 10W charger, this comes in the form of 5.1V x 2.1A. On the 12W charger, this is 5.2V x 2.4A. Typically the 10W chargers are sufficient for smaller devices such as the iPad Mini, while larger devices like the iPad Pro 12.9” need at least the 12W charger. More on that in a bit.

If you plug your iPhone into one of these larger adapters, it will charge faster. How much faster? Matt Birchler ran some testing, and from 0% over the course of an hour, the difference is roughly a 40% verses a 75% replenished battery. It is worth it, if you have access to these chargers, to use them.

Can you power your iPad with the Apple 5W charger? Sure. It’ll just take a long, long time. The iPad Pro 12.9” has a 10,307 mAh battery, roughly 6x the capacity of the iPhone 7. If you’re not actively using the iPad, it stands to reason it’ll take 6x as long to charger, and if you’re using the device while you’re charging it, it may not even be enough to keep the battery power indicator from dropping during usage.

So why does Apple stop at 12W as the biggest size stock charger? Because this is the effective limit for standard USB.

Fast charging with USB-C

With the release of the new MacBook, Apple moved away from MagSafe power adapters and over to USB-C for power delivery. The first one was released with a 29W USB-C power adapter, and soon after Apple released a more expensive USB-C to Lightning cable that could be consumed directly by the iPad Pro.

The 29W adapter outputs at 14.5V x 2.0A if operating at full delivery to a USB-C equipped device, or 5.2V x 2.4A (aka 12W) to a standard USB device.

There are some issues with using this charger for your iPhone.

  • It’s expensive. The USB-C to Lightning cable runs $29 from Apple, while the brick itself is $49.
  • Only the iPhone 8 and iPhone X will draw in the high (29W) delivery mode. Anything made before that and you’re effectively paying more for the same stock iPad (12W) charging ability.
  • The power brick is considerably larger than the 10W/12W iPad charger.
  • Lastly, it’s not been shown that the 29W is really necessary for even the iPhone 8 or the iPhone X. Matt’s testing, in addition to recent testing done by MacStories and MacRumors, showed a minimal delta between the 29W and a 12W adapter, which doesn’t seem worth it given the increased cost.

However, if you have an iPad Pro (especially the 12.9” version) the 29W adapter is downright awesome. If you use the iPad Pro as a true PC replacement, where it’s probable to run the battery down on the road with hours of continued use, then it’s worth spending the money on the faster recharging ability. If your iPad is secondary to your MacBook or other laptop, then keeping it topped up at night with the 12W is more than sufficient.

Third Party Chargers

If not Apple, Anker

Always buy from established brands, from established outlets. My personal favorite is Anker. They make a variety of really well built, nice looking chargers and certified Lightning cables. I have Anker car-chargers, multiple outlet chargers in my desks, and at my bedside. I keep a 5-port charger in my travel bag so I can have a central place to charge from hotel rooms when I’m traveling. Their entire line is available for purchase on Amazon. I probably own about as many Anker chargers as I do from Apple, and thus far nothing has not caught on fire.

Caveat emptor

Let the buyer beware. If you’re buying non-Apple charging devices, do your research. The first big warning involves the Lightning cables. Apple has a Made for iPhone (MFi) program that certifies the cables by embedding their controller chips into the connectors. While this results in more expensive cables, there is at least a standard that third-party vendors must meet to connect to the device in a safe way. This is unlike other mobile ecosystems where any cable can be used, with varied consequences.

However there is no certification program for the charger itself. Any product that outputs USB power, can charge your phone. That doesn’t mean you should use any charger that falls off the back of a truck. At best, you get lucky and don’t break your device. At worst, you burn your house down. Ken has a teardown of a counterfeit that shows that inside, there’s nothing much going on when compared to the real deal.

Multiple ports, single charger

All of Apple’s charging devices are designed to be one charger, plugged into one outlet, with a single iOS device connected to it. Most us have have a collection of USB chargeable devices, so it’d be nice to consolidate down to a single charger with multiple outputs. To do this, we look to third parties.

In addition to buying solid equipment, know what you’re buying. A dual-port USB power adapter that is advertised as 20W, cannot output 20W to each device. Even if it's USB-C, there are none on the market I've seen with this ability. The output details will typically show something like “5V x 4A (each 2.4A)” meaning each port can only deliver 12W of power to a single device, and if both are in use only 20W can be delivered in total. While this is probably more than sufficient for charging your iPhone and an Apple Watch, or even two iPhones, if you were attempting to charge two iPad Pro, it might be slow going.

Likewise, on a larger charger, depending on the device plugging in a device with a much lower power draw may cause all the ports to scale down their output. So a product advertised as a 60W charger might be fine to deliver 12W to your iPad Pro, and another 12W to your iPhone X, but if you attach your Apple Watch or AirPods to the charger, suddenly everything drops to 5W delivery without your awareness.

Anker markets their chargers with “PowerIQ” to independently delivery power to each port.

Qualcomm QuickCharge

In the Android ecosystem, Qualcomm has “enhanced” the USB specifications to deliver higher than standard USB output. This requires specific Qualcomm chips inside the phone, and in the charger. Apple devices will not charge any faster than 12W on these QuickCharge enabled power bricks, and neither will non-Qualcomm chipped Android devices. You can still utilize these power adapters on an iOS device, Anker makes many of them. They should not harm your iOS device in any way, but they’re not worth the additional cost if you don’t own a compatible device.

External battery packs

I own a variety of external USB battery packs. Mophie has been making these for a long time, but theirs tend to be more expensive for not a substantial difference in product aside from better material design. Anker makes a lot of them as well, at a reasonable price, but truthfully they tend to not be as nice looking.

My personal favorite at the moment though is the Belkin Pocket Power series, for a mix of price, battery capacity and clean external design. My primary pack, the Belkin Power Pocket 5000 mAh, allows me to charge my iPhone 7 multiple times before the battery needs to be replenished.

The pain with any external pack though is having to keep it charged, to be ready to use. Almost all of these packs utilize a microUSB input, which means packing another cable along side the Apple Lightning cable.

Again, 👀

Just as when utilizing third party power outlets, be sure what you’re plugging into. Stop at a gas station, or walk around any tech conference for more than 5 minutes and you’ll easily find cheap, portable USB battery packs to top up your phone on the go. My advise? Just say no.

Unless you’re in a truly bad situation, stick with established vendors for these products. Sticking some random battery in your pocket and letting it discharge into another device, without any question as to the stability of the product, seems like a bad idea. Refer back to the link around cheap and counterfeit wall chargers, with their lack of quality assurance, poor insulation, etc, and avoid a trip to the burn ward.

That said, the same rules about charging output apply to the battery packs, and complicate things by needing to account for their own input. The aforementioned Belkin battery pack has an output rating of 5V x 2.4A (12W) and an input rating of 5V x 2A (10W), so it’ll discharge (slightly) faster than it recharges. Likewise, watch multiple output ports, as the limitation of downscaling or having limited output for multiple devices is very common on some of the cheaper packs.

A multiple port AUKEY 20,000 mAh power bank I once bought rated 5V x 2.4A per port, but only 3.4A in total. Again, this means two devices attempting to charge from one pack will do it significantly slower. It’s not necessary bad, just something to watch.

Battery cases

I tend to dislike all forms of iPhone cases, unless they add some form of serious utility. The battery case is a perfect example of added such utility. There are only two that I have any first hand knowledge of, and those are the Mophie Juice Packs and the Apple Smart Battery Case. Comparing the two, the Mophie suffers from the same problem as the external batteries, in that they need microUSB to charge. Mophie isn't alone here, as a search on Amazon will result in a variety of packs with the same issue. microUSB.

The Apple case doesn’t suffer from this downside, having the advantage of being designed by Apple, it uses Lightning for input charging port. The iPhone 7 Smart Battery case adds an additional 2,365 mAh of capacity to the device. My wife has the 6S version on her phone nearly all the time. The real advantage though is that Apple also has software awareness of their pack, and is able to optimize the device accordingly.

Your iPhone behaves differently when it’s plugged into power, and when it’s in a third-party case, it doesn’t know it from being plugged into a wall outlet. You’ll likely get more bang for your mAh with the Apple case, in my opinion.

Personally, while I’ve tested both the 6/6S and 7 cases, they’re not something I want to leave on my device all the time as they add a considerable amount of bulk on days where I don't need all that capacity.

Topping Up

So we’ve talked about the basics of power delivery, the Apple options, the third party options, and what to do when you’re on the road. Now, when should you be taking advantage of all of these options? Whenever you can. If you start running low, plug it in. Don’t stress about charge cycles, over-charging, or wearing out the battery.

Apple uses high quality lithium ion batteries in their devices, backed with advanced power management software to make sure the devices don’t over charge or damage themselves. According to Apple, the device will fast charge up until 80%, and then trickle charge for the remaining 20%. Looking at this from a power perspective, I was able to view the draw using a USB multimeter. On an Apple iPad 12W charger, when the phone was near fully charged, it would draw at 5W.

More on Cases

As stated before, I generally avoid iPhone cases, but if you use them, consider what kind of case you have before using fast charging for extended periods of time. As someone who’s gone case-less for a long periods of time, one thing you notice is the device can get pretty warm when it’s plugged in. Energy being transmitted to the batteries will heat them up. It’s fine, but if you’re fast charging in a case, and you’re feeling the warmth of the battery through the case, just imagine what it’s like on the other side. In that situation, remove the case.


In summary:

  • Use the Apple iPad 12W charger, or a top quality third party high wattage charger, for the best combination of value and charging speed on your iPhone.
  • Always use Apple certified Lightning cables.
  • Anker makes great third-party charging accessories.
  • If you have an iPad Pro, the big 29W USB-C brick is great, but depending on your use may not be necessary.
  • Stick with known manufacturers for external battery packs.
  • If your battery is running low, plug it in.