Trust me, using any “unofficial” plug to charge your devices can land you in hot water. I learned this the hard way during a 7-day bicycle trip down south to Fukuoka. While soaking in a hot spring, I tried to sneak some juice for my phone but got caught immediately!
If you find yourself in need of a charge, head to McDonald’s! With locations everywhere–especially near train stations and in malls–they usually offer free plugs for charging your devices. You can also buy a battery-powered charger at any convenience store, but they can be pricey. So, it’s probably your best cost-effective solution to get a dollar coffee at McDonal’s and use the plug for as long as you need.