Can I use a 45w charger on my 4th gen iPad Air?

Yes - but some additional explanation may be helpful…

A compatible high-power USB Power Adapter is completely safe to use with your iPad; providing that the Power Adapter itself is healthy, it will not cause any issues whatsoever. That said, if a fault were to occur, the Power Adapter has the capacity to cause considerable damage to low-power electronics.

Apple’s current range of Power Adapter’s, including those intended for Mac computers, support USB PD (Power Delivery). USB PD is an active protocol; the source (Power Adapter) and sink/load (in this case, your iPad Pro) “negotiate” and agree a common Power Profile that will determine the charging voltage that will be applied. 

For non-PD compliant devices - or compliant devices that fail to negotiate a mutually supported Power Profile - the Power Adapter will only supply the standard USB 5V at a reduced current. This mechanism ensures that the higher charging voltages not supported by non-PD devices are not damaged by an over-voltage condition.

You should note that while your iPad Pro can be charged with a 45W (or other) Power Adapter, it will not charge any faster than when using the USB-C 20W Power Adapter that was likely supplied with your iPad. When charged with a USB-PD Power Adapter, the maximum iPad charging rate is limited to ~20W. When using a standard USB Power Adapter, operating at 5V, the maximum charging rate is limited to 12W (i.e., 2.4A @5V).

Where the higher-power Power Adapter does provide benefit is when being used with other USB devices via a USB hub. A higher-output Power Adapter provides a greater “power budget” - allowing other devices to receive power while maintaining the iPad’s maximum 20W charging rate. For example, a USB multiport hub may typically require 10W power; connected USB devices (external storage, keyboard, mouse etc) also draw additional power from the source. If the connected load exceeds the available supply, the iPad may not charge - or may charge at a substantially slower rate. In extremis, both the iPad and Power Adapter will share the connected load - and the iPad may actually discharge its battery to make-up the shortfall in available power from a connected Power Adapter.

You should note that while Apple devices generally support USB PD, they do not support other charging standards - such as QC (Quick Charge).

I hope this insight proves to be helpful to - in both confirming suitably of your proposed Power Adapter - and gaining a better understanding of factors that will impact charging of your iPad.

Vaeh_navi16 Said:

"Is 45w too much?: Can I use a 45w charger on my 4th gen iPad Air?"

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All is fine. You'll only get optimum use of the charger. Nothing will be faster.

For reference...

Toubleshooting iPad Charge:

A. Start Here: If your iPad won't Charge - Apple Support

B. Which Cables to Use: iPad Accessories - Power & Cables Power & Cables - Apple

C. Try what is on these Links:

• If your iPhone, iPad, or iPod touch won't Turn On or is Frozen - Apple Support
• If the Screen isn’t Working On your iPhone or iPad - Apple Support
• If your iPad won't Charge - Apple Support

D. Use an Apple Brand Cable:

Do not use a third party cable - cool though it may look, a fabric, third-part cable would likely tear - (Apple cable's are plastic and are intended for Apple).

E. About Battery Health:

Apple doesn't have Battery Health on an iPad. But, for note, Apple recommends that you get a new battery on an iPhone once its Battery Health reaches 80%.

F. A Faulty Device?:

So, is this covered under warranty? Note that this comes with a one-year, out-of-the-box, limited-warranty. So, set up a Genius Bar Appointment, asking them if this a faulty device.

It should be fine. All USB-C defaults to 5V to do negotiations, and then they won't negotiate more than the iPad model can accept. Even then, the power adapter is really just a voltage source, and the power management circuits inside the iPad control the input current.

I'm wondering if there's anyone who used a USB current/voltage tester to see what input voltages various iPad models actually support.

The 20W Apple USB-C power adapter is only 5V/3A or 9V/2.22A. I would assume that all iPad models with native USB-C can handle 9V. But I have used an aftermarket 20W USB-C power adapter that has 5/9/12V. My Apple 30W USB-C power adapter has 5/9/15V, and a few 45W ones in my home have 5/9/12/15/20V. Obviously whatever power input is going to be converted to a voltage that can operate an iPad and charge the battery, which is going to be under 5V. The higher voltages just allow more power with less current going through the cable, but it still needs to be converted to a lower voltage by the iPad.

TheLittles wrote:

D. Use an Apple Brand Cable:

Do not use a third party cable - cool though it may look, a fabric, third-part cable would likely tear - (Apple cable's are plastic and are intended for Apple).

E. About Battery Health:

Apple doesn't have Battery Health on an iPad. But, for note, Apple recommends that you get a new battery on an iPhone once its Battery Health reaches 80%.

I've used third-party cables extensively. Apple doesn't have a USB-A to USB-C cable so I'm stuck with non-Apple. I have noticed varying quality though. But I would never pay for an Apple USB-C cable just for an iPad. There's good stuff out there like cables from Anker, Belkin, Amazon, Monoprice, etc. Some have fabric coverings that have worked well for me, but the fabric is not the jacket - it's typically on top of the actual jacket. And I've seen Apple cables with frayed jackets. Apple also used fabric on some cables like new MagSafe 3 cables.

There are some tools that can be used to get an idea what the battery health is, like coconutBattery for Mac. But the number will go up and down. I remember when the Battery Life app from the App Store did something similar before Apple discontinued its ability to tap into the battery health internals. And Apple obviously can peek at the battery health with an official diagnostic. Once I was thinking i might need a battery replacement service (really just a full replacement) and an Apple employee showed me that it was indicating 90% battery health.

y_p_w:

Based on personal experience...

A. Use of Their Party Cables:

I've used third-party cables too --not all work fast and, some just don't work. But, it may work just fine.

B. 80% Battery Health:

You're right. The Battery Health is just a guestimation on Apple's part. But, stick with the 80% rule, as a thumbs up for it being time for a new battery.

TheLittles wrote:

y_p_w:

Based on personal experience...

A. Use of Their Party Cables:

I've used third-party cables too --not all work fast and, some just don't work. But, it may work just fine.

B. 80% Battery Health:

You're right. The Battery Health is just a guestimation on Apple's part. But, stick with the 80% rule, as a thumbs up for it being time for a new battery.

I know with aftermarket USB-C cables there's just way too much variation. But I also consider them to be consumable - either through loss, wear, or failure. I dropped my mini 6 when it was charging and my favorite USB-A to USB-C cable was trashed when the connector tip bent. I've had a few that don't work very well and might be worth tossing. Some of the cheapest ones I have are rock solid. There doesn't seem to be any correlation between price and quality. Heck - I had one that I bought at a dollar store that worked every time but then I forgot it on a bus ride. When it costs less than $2 who cares. And I like having a lot of them too. Some are even short ones that I'll use with a USB power pack. I know there's also a variation in rated current, but the vast majority (and what Apple provides for iPads) are 3A. I've bought a few 5A ones but the odd thing is that none are marked on the cable. I don't think I've paid more than $5 for a USB-C cable, and those were usually ones I wanted to be heavier duty for use with a computer. My current favorites for every day use are one that came with an Amazon Fire HD tablet (that was damaged) and a Monoprice Essentials 5A rated cable. The latter is really beefy and cost me less than $4.

With MFi Lightning cables the quality can be all over the map. But I've bought them as cheap as $6 for a 5-pack.

I like these cheap cables because I have them everywhere - in my car, my bag, my pocket, bedside, hooked up to my computers, etc. I've bought 15 Lighting cables for about the price of a single Apple OEM version. I'm a little bit wary of cheap USB-C cables, but I've had good results with some cheap cables.

As far as battery replacements go - Apple's general iPad policy is that the battery replacement is just replacement with a service unit. I've tried going through that before, and they did a thorough check for major cosmetic damage and or a bent case, as well as a diagnostic. That was the time they found it at 90%. Since it's essentially a trade in for a unit that's ostensibly in better physical condition, they're not likely to just replace it on demand. But they will require the same 80% or below that's the general rule for all Apple device battery service. Not sure about iPhone though.

Yes, you can use a 45 watt power adapter (or even larger). The iPad will not draw more power than it is designed for.