As the battery ages, the drain gets worse and worse.
Tips
usage
Colloquial tech complaint word for phones, laptops, earbuds. Often intensified: 掉电快, 特别掉电, 掉电严重. Not used for 'to power off normally' — that's 关机.
memory
掉 (to drop/fall) + 电 (electricity) — electricity 'falling away' from the battery. The same 掉 appears in 掉线 (to lose connection) and 掉色 (to lose color).
