Thanks to the iPhone's reserve power feature, if you have set up a Suica issued with the Welcome Suica Mobile app as an Express Transit card , you can use your Suica for up to five hours after your phone powers down automatically in need of a recharge. However, this function is unavailable if you turn off the power to your device yourself. 

*If this is the first time you issue a digital Suica card on your device, it will be set as your Express Transit card automatically. 
*Apple Watch does not have a backup power function. 
*If your device runs out of power before you exit the ticket gate (while in transit), please refer to this link (https://apfaq.mobilesuica.com/faq/show/6907?site_domain=wsm).