Every iPhone 18 Pro Max leaves the factory with its battery capped below 20 watt-hours (Wh) by firmware. That limitation comes off when the owner activates the phone. Apple has explained the arrangement in a support document.
The cap exists because of the battery’s size. The iPhone 18 Pro Max is the only iPhone with a single battery cell rated above 20Wh. The version with a physical SIM tray, which is what most Kenyan imports will be, has a 5,391 mAh cell. The eSIM-only version sold in the US and eleven other markets has 5,567 mAh. Milliamp-hours measure charge. Multiply mAh rating by the cell’s rated voltage of 3.907V and you get energy in watt-hours: 21.06Wh for the physical SIM model and 21.75Wh for the eSIM model.
That extra capacity is part of why Apple quoted 45 hours of video playback for the Pro Max at launch.
Why 20Wh matters
Dangerous goods rules for air, sea and road transport treat lithium-ion cells differently depending on whether they are above or below 20Wh. A phone with a smaller cell ships under exceptions that cover almost every handset. A cell above 20Wh makes the shipment fully regulated, with specific packaging, labels and paperwork. The US Department of Transportation’s hazardous materials regulator sets this out in its lithium battery guide for shippers.
Android makers have dealt with the limit in two ways. Some split the battery into two cells, each under 20Wh. Others ship a smaller battery to Europe. OnePlus did the second with the Nord CE 4 Lite in 2024, which had 5,500 mAh in India and 5,110 mAh in Europe.
Apple kept one cell and the full capacity, but handles the rules using software magic. By our calculation, 20Wh is about 5,119 mAh at 3.907V. So a boxed physical SIM Pro Max can hold under 95 percent of its full charge, and a boxed eSIM model under 92 percent.
Prepare to Ship
If you’re wondering, well this is cool, but what happens when I want to ship my own already activated device? Well, you can bring the limitation back. Apple has added a Prepare to Ship option under Settings, General, Transfer or Reset iPhone. It drains the battery below 20Wh and sets a charge limit so the phone stays there in transit. Discharging can take a few minutes, or up to a couple of hours from a full charge, and the phone may run warmer than usual while it happens.
Apple says the battery is safe for air travel and that Prepare to Ship is not needed when you carry the phone on a trip. No other iPhone model needs this feature.
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