A smart charging circuit that automatically cuts off power once a mobile phone is fully charged (current drops below 0.450 A), using: Current sensor (ACS712) SPDT relay or P-channel MOSFET for switching Arduino Uno for processing Two versions of the circuit were tested: With relay: net loss of 0.178 Wh With MOSFET: energy saved = 0.503 Wh Though initially designed to save energy, the real value lies in battery safety and longevity. 

Key Features & Insights Threshold current: 0.450 A triggers disconnection. Phones tested: Samsung Galaxy A31, iPhone 8. Trickle charging after 100% contributes to battery heating and degradation. Energy saved (annual projection): Per user: ~3.6 kWh/year For 760M Indian users (2021): ~2,700 GWh/year ≈ 78% output of a 500 MW thermal power plant Secondary Benefits 🔥 Safety Overcharging raises battery temperature by ~44°C Risks: wire heating, Li-ion plating, CID (current interrupt device) failure, and even battery explosion 🔋 Battery Life Extension Higher charging temps reduce lithium-ion battery cycle life Studies show capacity degrades faster at 85–120°C Detailed Calculations Energy model: Before cutoff: Significant trickle charge continues After cutoff with MOSFET: Clear savings in Wh Temperature model: After 5 hours of overcharging: ~44°C rise Future Scope Expand device for laptops, TVs, and other high-power vampire devices Integrate into IoT-enabled smart homes References Stanford Magazine on Vampire Energy Battery University – Li-ion Charging Safety Energy Usage Stats (LBNL) Research on Battery Degradation