• 電気でんき — electricity
• 電話でんわ — telephone
• 電車でんしゃ — train
• 電池でんち — battery
• 電波でんぱ — radio wave
• 電源でんげん — power source
• 充電じゅうでん — charging (a battery)
• 発電はつでん — power generation
• 漏電ろうでん — electric leakage

電 originally points to lightning in storm clouds (雨). Today it also means “electricity,” so it shows up everywhere — phones, trains, batteries, signals, and daily power use.