Juli Clover:

The iPhone 18 Pro Max has a battery capacity over 20 watt-hours, which means there are additional shipping requirements. If an iPhone 18 Pro Max needs to be shipped somewhere, its maximum battery capacity has to be limited through firmware.

[…]

Customers who need to ship the iPhone 18 Pro Max for repair, trade-in, or other purposes have to use a new Prepare to Ship feature. Prepare to Ship discharges the battery to below 20Wh and sets a charge limit so the iPhone stays below the threshold during the shipping process.

Laptops, of course, have larger batteries, but they aren’t affected because each cell is below the limit.